feat: add "get-versions" command to replace "orchestrators"

[mboersma]

Reason for Change:

The aks-engine orchestrators command is still generic and returns DCOS versions, for example, although aks-engine is Kubernetes-only.

This hides the orchestrators command and adds a get-versions command that calls the same code with the orchestrator argument hard-coded as Kubernetes.

There wasn't a consensus in #339 as to the name of the new command, so this is just my proposal, but I'm happy to change it based on your feedback.

Issue Fixed:

Fixes #339

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

I tried to use Cobra's "alias" feature to avoid writing any code, but it didn't quite fit since the commands don't expose the same arguments. Hiding the orchestrators command but otherwise leaving it intact seems like the most polite way to replace it with a new command.

[CecileRobertMichon]

I like get-versions

lgtm

[CecileRobertMichon]

any relevant documentation that should be updated?

I know there's at least one reference to the orchestrators command in upgrade.md

[codecov]

Codecov Report

Merging #448 into master will increase coverage by 0.02%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##           master     #448      +/-   ##
==========================================
+ Coverage   53.43%   53.46%   +0.02%     
==========================================
  Files          95       96       +1     
  Lines       14391    14406      +15     
==========================================
+ Hits         7690     7702      +12     
- Misses       6038     6040       +2     
- Partials      663      664       +1

[mboersma]

any relevant documentation that should be updated?

I'll fix upgrade.md and do a general search for references to the orchestrators command.

Edit: docs are updated.

[mboersma]

Here's what the help looks like after this PR:

$ ./bin/aks-engine help
AKS Engine deploys and manages Kubernetes clusters in Azure

Usage:
  aks-engine [flags]
  aks-engine [command]

Available Commands:
  completion    Generates bash completion scripts
  deploy        Deploy an Azure Resource Manager template
  generate      Generate an Azure Resource Manager template
  get-versions  Display info about supported Kubernetes versions
  help          Help about any command
  scale         Scale an existing Kubernetes cluster
  upgrade       Upgrade an existing Kubernetes cluster
  version       Print the version of AKS Engine

Flags:
      --debug                enable verbose debug logs
  -h, --help                 help for aks-engine
      --show-default-model   Dump the default API model to stdout

Use "aks-engine [command] --help" for more information about a command.

$ ./bin/aks-engine get-versions --help
Display supported Kubernetes versions and upgrade versions

Usage:
  aks-engine get-versions [flags]

Flags:
  -h, --help             help for get-versions
      --version string   Kubernetes version (optional)
      --windows          Kubernetes cluster with Windows nodes (optional)

Global Flags:
      --debug   enable verbose debug logs

[mboersma]

Output of the command is identical to aks-engine orchestrators --orchestrator Kubernetes (which still works but doesn't show up in aks-engine help):

$ ./bin/aks-engine get-versions 
{
  "orchestrators": [
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.6.9",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.7.15"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.7.16"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.7.15",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.7.16"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.8.14"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.8.15"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.7.16",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.8.14"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.8.15"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.8.14",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.8.15"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.9.10"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.9.11"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.8.15",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.9.10"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.9.11"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.9.10",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.9.11"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.10.9"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.10.12"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.9.11",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.10.9"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.10.12"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.10.9",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.10.12"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.11.6"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.11.7"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.10.12",
      "default": true,
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.11.6"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.11.7"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.11.6",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.11.7"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.12.4"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.12.5"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.11.7",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.12.4"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.12.5"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.12.4",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.12.5"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.13.2"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.13.3"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.12.5",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.13.2"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.13.3"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.13.2",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.13.3"
        },
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.14.0-alpha.1"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.13.3",
      "upgrades": [
        {
          "orchestratorType": "",
          "orchestratorVersion": "1.14.0-alpha.1"
        }
      ]
    },
    {
      "orchestratorType": "Kubernetes",
      "orchestratorVersion": "1.14.0-alpha.1"
    }
  ]
}

[jackfrancis]

/lgtm

[jackfrancis]

As a follow-up PR, we should clean up the output.

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