This introduces the reviewboard.reviews.testing.queries.review_groups

module for query-building functions for tests. It contains the following

methods:

get_review_groups_accessible_q()
get_review_groups_accessible_prep_equeries()
get_review_groups_accessible_equeries()
get_review_groups_accessible_ids_equeries()

These generate expected Q objects and queries that matches calls to

Group.objects.accessible() and Group.objects.accessible_ids().

They're written in a verbose manner that ensures we only ever test

against finalized Q expressions, to minimize chances of regressions or

unexpected behavior.
The unit tests for .accessible() and .accessible_ids() have been

completely rewritten. They now check against these expected queries, but

they've also been expanded considerably to more thoroughly check access

with positive and negative test data, to better catch regressions. The

approach being used here will be carried over to other accessibility

tests for the next batch of this peformance work.

Unit tests pass.