simplify switchcase for rabbitmq plugins command

[jklare]

Proposed Changes

Use new method installed_rabbitmq_version to simplify switchcases
for plugins command.

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
• Cosmetics (whitespace, appearance)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

[michaelklishin]

Thank you!

[chalb]

I really like this PR. Quick question: When will this be released?

[michaelklishin]

No earlier than we have some feedback and decision made for #521.

[chalb]

Fair enough. Thank you for your advise!

[michaelklishin]

So #521 is addressed as far as I'm concerned. I'd appreciate some sanity checking of the tip of the v5.x branch, then we can produce a new patch release.