Refs #7423: Convert to using Bastion core to provide the Katello UI.

This commit removes the components that have been transitioned to Bastion
core and changes the engine to bastion_katello. Further, dependencies
in both the re-named engine and Katello are removed that no longer apply.
Refs #7733: Remove usage of Host fixtures in favor of Host factories.

Foreman is moving to the use of factories for testing and removing
the host fixtures from usage. Here we change out our reliance on
those host fixtures in favor of the factories.
Merge pull request #4754 from ehelms/refs-7423

Refs #7423: Convert to using Bastion core to provide the Katello UI.
Merge pull request #4757 from ehelms/refs-7733

Refs #7733: Remove usage of Host fixtures in favor of Host factories.