Add Katello namespace to Authorization::Provider

Fixes an error that occurs when using katello_api at
https://github.com/Katello/katello_api/pull/13 to generate v2 API
documentation for the changes I made to the ProductController in
https://github.com/Katello/katello/pull/3479
Merge pull request #3489 from mkelley33/katello-namespace-provider

Add Katello namespace to Authorization::Provider