This splits out the permission lookups from the review group equeries

into get_user_permissions_equeries() in

reviewboard.accounts.testing.queries.
The review group and review request equeries have been updated to take

flags indicating whether permission lookup queries are expected. This

would be disabled if they've already been fetched by this point (since

they're cached).
There's a little bit of related cleanup in parts, changing where some

logic (e.g., superuser checks for review group access queries) lives and

better reusing state from expected Q results for prep equeries. These

will be important for upcoming changes.

All unit tests pass.