Fixes #38040 - Clear retain_version_count when mirroring policy is not additive

[sjha4]

What are the changes introduced in this pull request?

1. On the API, clear out retain_package_versions_count when mirroring policy is anything other than additive
2. Add a validation on root model to make sure retain_package_versions_count is only set when mirroring policy is additive.

Considerations taken when implementing this change?

What are the testing steps for this pull request?

1. Create a yum repo with some retain_package_versions_count and mirroring policy as Additive
2. Sync
3. Now update mirroring policy to Content only/Complete and sync again.
4. You'll see an error.
5. In console if you check repo.root.retain_package_versions_count it will still have the value from step 1

With this change,
In step 4 you'll not see the sync error
In console if you check repo.root.retain_package_versions_count you'll see nil

We can also test the validation by doing so in console:

repo.root.mirroring_policy = "mirror_complete"
repo.root.retain_package_versions_count = 3
repo.root.valid? # false
repo.root.errors.messages # {:retain_package_versions_count=>["cannot be set for repos without 'Additive' mirroring policy."]}

[qcjames53]

I have confirmed that errors are thrown appropriately when changing the mirroring policy to an invalid option in the UI, hammer, API, and in the rails console. The validation works for both setting an invalid mirroring policy with a versions count set and for setting a versions count with an invalid mirroring policy set. The logic looks okay to me and I'm happy with the test case changes. I had one nitpick on line length; once that's fixed feel free to merge!

ACKed.

[qcjames53]

This line is REALLY long. Would you mind splitting it up?

[sjha4]

@qcjames53 : Updated for readability..