Engine: test fixes after rebase with devel branch

This commit contains fixes that are needed to ensure
'rake test:katello' runs successfully after the rebase
of engine branch with devel branch.

Note: the changes to the models to incorporate 'class_name'
were required to support the association_test which
treats model associations as the base model
(e.g. Provider) vs the namespaced model (e.g. Katello::Provider).

Results with commit were:
test: 1082 tests, 2082 assertions, 0 failures, 0 errors, 5 skips
spec: 1283 tests, 2477 assertions, 0 failures, 0 errors, 4 skips