Fix the last remaining failures.

* bzrlib/tests/test_server.py:
(TestingSmartServer.serve): Run the hooks.
(SmartTCPServer_for_testing.stop_server): Don't forget the chroot
server.

* bzrlib/tests/per_branch/test_push.py:
(EmptyPushSmartEffortTests.setUp): Fix the issubclass check, the
smart test server don't ihnerit directly from
server.SmartTCPServer anymore.