Because two things called `BaseTestCase` is quite confusing.
I haven't bothered refactoring the other `BaseTestCase` because
that disappears anyway when we drop Python 2.6 support.
Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Ensure setup_module is called at session level, making the test
suite not order dependent. Test files can be invoked independently.
Signed-off-by: Joffrey F <joffrey@docker.com>