Clean up the reviewtags tests and move into reviewboard/reviews/tests/.
Review Request #9179 - Created Sept. 7, 2017 and submitted
This reorganizes the tests in the reviewtags test suite, moving to
per-tag test suites, and simplifying the function names accordingly. It
also moves those tests into
reviewboard/reviews/tests/, so that all
unit tests for the reviews module live in one place.
Unit tests pass.