Clean up the reviewtags tests and move into reviewboard/reviews/tests/.

Review Request #9179 - Created Sept. 7, 2017 and submitted

Christian Hammond
Review Board

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.

David Trowbridge
Christian Hammond
Review request changed

Status: Closed (submitted)

Change Summary:

Pushed to release-3.0.x (ddf740c)