Ensured that the test suite creates the default DB before any others.

Refs #14799. Technically this fixes the problem, but I'm far from convinced
it's the perfect solution, so I'm leaving the ticket open. I'm committing
this now because it's the minimum required to get the test suite running
again, but this commit can -- and probably should -- be reverted in favor of
a more holistic fix later on.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14756 bcc190cf-cafb-0310-a4f2-bffc1f526a37