Fix :clear_permissions action in user provider

[TheFLHurricane]

Proposed Changes

529 :clear_permissions action for user provider is not executed in some cases when it should

:clear_permissions fails to ever trigger in user provider because a user with permissions can never have a true result against a nil perm_list that is passed to the user_has_permissions? method, which is necessary to trigger the action. Fixing this by changing check method to check if correct permissions exist and not just any permissions.
Specific details:

1. Change result of first return (perm_list.nil? && cmd.stdout.empty?) from false to true
2. Change action :clear_permissions to call if method instead of unless method
3. Change name of method from user_has_permissions? to user_has_correct_permissions? to accurately reflect result being returned

Types of Changes

What types of changes does your code introduce to this project? Put an x in the boxes that apply

• [x ] Bug fix (non-breaking change which fixes issue #529 )
• [ ] 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

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• [x ] I have read the CONTRIBUTING.md document
• [x ] 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
• [x ] I have added necessary documentation (if appropriate)
• [x ] Any dependent changes have been merged and published in related repositories

Further Comments

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[michaelklishin]

Thanks. We need to add some tests. I've submitted #531 with minor modifications, let's continue there.