Remove fakeclient and use testenv for flux cmd tests

Remove use of the fake client, and replace with a real client connected to the
testEnv.

This required fixes to the yaml files as the testEnv has stricter verifcation
of objects. This also meant it was not possible to test a GitRepository with
a missing artifact since that is not a valid state.

The tests are slower than before, taking around 7-10 seconds each because the
 testEnv is setup and destroyed for every test. These will be sped up in a
 follow up PR.

Signed-off-by: Allen Porter <allen@thebends.org>