Added CLI tests for Docker images.

Added two new CLI tests for creating repositories that use Docker
content. Please see #1550 and #1551 for more information about naming
conventions for Docker repositories. Please note that the existing
synchronization tests are affected by [Bugzilla #1152237](https://bugzilla.redhat.com/show_bug.cgi?id=1152237).

Also removed several Bugzilla decorators as the referred issues had
already been verified and tests were being run.

Finally, updated ``test_positive_update_1`` test as it was trying to
update ``FAKE_1_YUM_REPO`` to ``FAKE_1_YUM_REPO`` and assert that the
URL had been updated :)

All tests pass against nightly build (with some skips due to Bugzilla.)
When this assertion fails, the user will not be told what the actual content type is. Can this error message be amended or dropped?