Skip some activation key tests due to BZ 1127335

Elasticsearch is used to index new activation keys when they are created.
Unfortunately, elasticsearch cannot keep up when the system is under heavy load.
Make `ActivationKey.read_raw` only re-try a read upon receiving a 404 if
bugzilla bug 1127335 is open. Add the the `skip_if_bug_open` decorator to all
appropriate tests in module `test_activationkey`.
This change is unrelated to the issue at hand. I just looked at the code and decided that it could be trimmed down.