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.)
I see `url` and `content_type` used in assertions below, but not name.