support concrete schema version

[yangcao77]

Signed-off-by: Stephanie yangcao@redhat.com

What does this PR do?:

support concrete schema version,
get latest devfile api and schema

Which issue(s) this PR fixes:

Fixes devfile/api#625

PR acceptance criteria:

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Open new test/doc issues under the devfile/api repo
• Check each criteria if:
• There is a separate tracking issue. Add the issue link under the criteria
  or
• test/doc updates are made as part of this PR
• If unchecked, explain why it's not needed

• Unit/Functional tests

• QE Integration test

• Documentation

• Client Impact

How to test changes / Special notes to the reviewer:

run unit tests
or parse devfile with a concrete schema version

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: maysunfaisal, yangcao77

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [maysunfaisal,yangcao77]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment