Add a subcollection under VMs for displaying CD-ROMs

[skateman]

This is required for the API-driven reconfigure VM screen where the user has to display the related CD-ROMs. Any change is going through the VmReconfigureRequest model that is already supported by the API, therefore, there's no need for anything else than GET.

GET /api/vms/2/cdroms
{
  "name": "cdroms",
  "count": 1127,
  "subcount": 1,
  "pages": 2,
  "resources": [
    {
      "href": "http://localhost:3000/api/vms/2/cdroms/4"
    }
  ],
  "links": {
    "self": "http://localhost:3000/api/vms/2/cdroms?offset=0",
    "next": "http://localhost:3000/api/vms/2/cdroms?offset=1000",
    "first": "http://localhost:3000/api/vms/2/cdroms?offset=0",
    "last": "http://localhost:3000/api/vms/2/cdroms?offset=1000"
  }
}


GET /api/vms/2/cdroms/4
{
  "href": "http://localhost:3000/api/vms/2/cdroms/4",
  "id": "4",
  "device_name": "CD/DVD drive 1",
  "device_type": "cdrom-image",
  "location": "1:0",
  "filename": "[]",
  "hardware_id": "5",
  "mode": null,
  "controller_type": "ide",
  "size": null,
  "free_space": null,
  "size_on_disk": null,
  "present": true,
  "start_connected": false,
  "auto_detect": null,
  "created_on": "2017-10-06T16:41:11Z",
  "updated_on": "2017-10-06T16:41:11Z",
  "disk_type": null,
  "storage_id": null,
  "backing_id": null,
  "backing_type": null,
  "storage_profile_id": null,
  "bootable": null
}

@miq-bot add_label hammer/no, changelog/yes
@miq-bot add_reviewer @abellotti
@miq-bot add_reviewer @lpichler

[skateman]

Same problem as with #598 and no idea how to fix it 😞

[lpichler]

@skateman This branch has conflicts that must be resolved.

[skateman]

@miq-bot rm_label unmergeable
@lpichler fixed

[miq-bot]

Checked commit skateman@89022b0 with ruby 2.3.3, rubocop 0.69.0, haml-lint 0.20.0, and yamllint 1.10.0
3 files checked, 0 offenses detected
Everything looks fine. 👍