Fixed #15554 -- Corrected test failure in contenttypes when default site isn't...

Fixed #15554 -- Corrected test failure in contenttypes when default site isn't example.com. Thanks to twil for the report, and PaulM for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15766 bcc190cf-cafb-0310-a4f2-bffc1f526a37