Description of problem:
As a user I'm unable to find which content view is preventing repository from being deleted
if repository is included to removed version of content view which was included into composite
content view (yeah, it was complex, I know ).

Steps to Reproduce:
1. Create repository X;
2. Create content view A;
3. Include repository X to content view A;
4. Publish content view A to library;
5. Create composite content view B;
6. Include content view A to composite content view B;
7. Publish content view B to library;
8. Remove all versions of content view A;
9. Try to remove repository X.

Actual results:
RuntimeError: Repository cannot be deleted since it has already been included in a published Content View.
Please delete all Content View versions containing this repository before attempting to deleting it.

Expected results:
Either indicate content view id which is preventing repository removal or
prevent content view versions from being deleted if it was included into composite content view.

Additional info:

1. hammer content-view list
   can't help in this situation as it was not showing repository ids for composite content views.

1. rpm -qa | grep katello
   katello-installer-base-2.2.2-1.el7.noarch
   katello-service-2.2.1-0.el7.noarch
   katello-debug-2.2.1-0.el7.noarch
   katello-selinux-2.2.1-1.el7.noarch
   katello-common-2.2.1-0.el7.noarch
   katello-server-ca-1.0-2.noarch
   katello-certs-tools-2.0.1-1.el7.noarch
   katello-default-ca-1.0-1.noarch
   katello-agent-2.2.1-1.el7.noarch
   rubygem-hammer_cli_katello-0.0.14-1.el7.noarch
   katello-2.2.1-0.el7.noarch
   ruby193-rubygem-katello-2.2.2-2.el7.noarch
   katello-installer-2.2.2-1.el7.noarch
   pulp-katello-0.4-1.el7.noarch