This introduces reviewboard.reviews.testing.queries.reviews, which

provides the following functions for building expected queries and

Q-expressions:

get_reviews_accessible_q()
get_reviews_accessible_equeries()
get_reviews_from_user_q()
get_reviews_from_user_equeries()

This covers all the queries made in ReviewManager, giving us what we

need for any unit tests that need to check accessible reviews.
The ReviewManager unit tests have been updated to use these,

simplifying that code considerably.

Unit tests pass.