Re-enable tests that are disabled due to missing or offline fixtures

[dralley]

We have a couple of tests that either never had a fixture made available for them, or did at one point but the fixture went offline. Those tests are now skipped.

We should re-enable as many of them as possible by generating new fixtures to handle those same scenarios. Note that in some cases it may be easier to do so using createrepo_c via Python code than by messing with createrepo_c on the command line.

https://github.com/rpm-software-management/createrepo_c/blob/master/examples/python/simple_repository_writing.py