Merge pam-test-cleanup-6316: Cleanup pam tests.

Author: tom.prince
Reviewers: rwall
Fixes: #6316

There is a pyflakes error, as well as an open-coded
TestCase.patch. This cleans them up.

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@37817 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb