Fixed #17903 -- Inactive users shouldn't have any permissions.

See [#17903](https://code.djangoproject.com/ticket/17903).
I was thinking to assign the group permissions at the beginning of the test case so you can check all three together and not need the second round of tests along with setting the user back to `is_active=True`. Also, `codename='test_(user|group)'` would be helpful.