906859-import-messages - cleaned up error messages for both import and delete manifest

Minitest is skipped until non-private manifests can be created to excercise the code and be checked into git
Destroy default content view on cascade when deleting environment

Also validate the default content_view explicitly. Here is what happened
without this changes:

1. Create environment (default content view and content_view_version
was crated)
2. Delete the environment (`content_view` stayed there because
`:dependent=> :destroy` was missing)
3. When creating an environment with the same name, the content_view
was not created, because another content view with the same name
already existed. However, because the content_view was being saved as
part of saving content_view_version, the exception was not thrown (and
the content_view_version was saved successfully without association to
any content_view)
4. When promoting some time after this incident (that happened
unnoticed), "nil pointer exception" occurred while promoting, because
the default content view was not there.
add gems from SC ruby193 to comps
Merge pull request #1750 from xsuchy/pull-req-ruby193-foreman

add gems from SC ruby193 to comps
Automatic commit of package [katello-cli] release [1.3.5-1].
Merge pull request #1704 from thomasmckay/906859-import-messages

906859-import-messages - cleaned up error messages for both import and delete manifest
Merge pull request #1743 from iNecas/default-content-view-dependent-destroy

Destroy default content view on cascade when deleting environment