Update to use more of Djblets's new API and testing support.

Review Request #7499 — Created July 7, 2015 and submitted — Latest diff uploaded

Information

Review Board
release-2.5.x
9d7d7fd...

Reviewers

More of Review Board's code has moved into Djblets in recent changes,
which allows us to remove a lot of code from Review Board. This impacts
the API resources and the unit testing code.

It also removes a redundant call to initialize() in the base API
testcase, which is already called in the base Review Board testcase.

All unit tests pass.