fixes #5184 - extend foreman host to provide association to katello content host

This commit provides for a few small changes:
1. add an association to the foreman host to the katello content host
2. update the foreman defacing to use the data from this association
   versus querying the System table for the details
3. when a content host is registered, if there exists a foreman host
   with the same hostname, associate the two (host & content host)
4. with the relation added in #1, when the foreman host is deleted
   the corresponding content host will be deleted.
refs #5184 - rename 'remove' to 'unregister' for content host ui
fixes #5800 - host collections ui - errors on add/remove should be displayed
Fixes #5574 - consider 301 as correct response for the cdn path

But check for `repodata/` instead of `repodata` as that's what we want
in the first place.
Merge pull request #4115 from bbuckingham/issue-5184

fixes #5184 - extend foreman host to provide association to katello content host
Merge pull request #4156 from iNecas/1099221

Fixes #5574 - consider 301 as correct response for the cdn path
Merge pull request #4153 from bbuckingham/issue-5800

fixes #5800 - host collections ui - errors on add/remove should be displayed
Fixes #5940/BZ1080361, show loading indicator for content view versions.
Merge pull request #4157 from waldenraines/5940

Fixes #5940/BZ1080361, show loading indicator for content view versions.