Publish tests for modulemd/modulemd

[pulpbot]

Author: @fao89 (fao89)

Redmine Issue: 6427, https://pulp.plan.io/issues/6427

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• the final module.yaml should be compressed in repodata directory
• no error if not all artifacts are present

[dralley]

More broadly, this should be "metadata integrity tests" - that is, verifying that the yaml coming out matches what is expected