Fixed #16686 -- Reduced time to wait for cache expiration in a test to...

Fixed #16686 -- Reduced time to wait for cache expiration in a test to alleviate race-condition-y effects.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16728 bcc190cf-cafb-0310-a4f2-bffc1f526a37