The repository API unit tests were pretty ancient and crufty, and the

helper functions made a lot of assumptions about what was needed for

repository testing and creation that just didn't hold up anymore (mainly

that repositories were never going to be backed by hosting services). On

top of this, we overrode all kinds of class-level functions directly,

without using kgb, which wasn't very safe.
This cruft is blocking work on finally getting this API into shape to

allow creation of repositories backed by hosting services.
This change cleans up the tests, removing some of the bad assumptions,

making the helper functions more generally useful, moving code to kgb,

and otherwise just simplifying the tests.

Unit tests pass.