Code to promote/publish content views with docker repos

Note this PR relies on https://github.com/Katello/katello/pull/4732 getting merged.
Right now  we do not have a way to add docker repositories in the UI and you will have to use hammer cli. Here is a sample set of steps.
```
$ hammer repository list --organization-id=3 --content-type=docker

---|-------------------------|------------------------|--------------|------------------------------------------------------------------
ID | NAME                    | PRODUCT                | CONTENT TYPE | URL                                                              
---|-------------------------|------------------------|--------------|------------------------------------------------------------------
29 | fedora/rabbitmq         | great                  | docker       | https://registry.hub.docker.com/repos                            
---|-------------------------|------------------------|--------------|------------------------------------------------------------------

$ hammer content-view create --name=test-pub --organization-id=3
$ hammer content-view add-repository  --name=test-pub --organization-id=3  --repository-id=29
$ hammer content-view publish --name=test-pub --organization-id=3

```