Fixed #15035 -- Fixed collectstatic management command to work with non-local...

Fixed #15035 -- Fixed collectstatic management command to work with non-local storage backends correctly. Also refactored a bit code smell.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15154 bcc190cf-cafb-0310-a4f2-bffc1f526a37