Update the RB-Gateway tests to use the new hosting service test helpers.
Review Request #9870 — Created April 10, 2018 and submitted
This updates the RB-Gateway 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.