Fix test setup loophole
Fix test setup loophole

Currently we attempt to enforce that super().setUp() is called from all
our test classes that override setUp(). We do this by making an
assertion in tearDown(). The loophole: if the test class overrides both
setUp() and tearDown(), the assertion will never be made.

This change closes the loophole, making it much harder to accidentally
subvert this check.

nickzuber/ClusterRunner,Medium/ClusterRunner,josephharrington/ClusterRunner,josephharrington/ClusterRunner,box/ClusterRunner,box/ClusterRunner,nickzuber/ClusterRunner,Medium/ClusterRunner