Update the Gerrit tests to use the new hosting service test helpers.

Review Request #9775 — Created March 14, 2018 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x
678d883...

Reviewers

This updates the Gerrit test suite to use the new helpers for hosting
service unit tests, which provide better, more consistent checks with
simpler code. The results of all HTTP requests are checked, ensuring
we're calling what we expect and that behavior doesn't change in the
future.

Unit tests pass.