Merge ssl-client-endpoint-parser-test-5801-2: Add missing test coverage for SSL client endpoint string description parser

Author: ecnahc515
Reviewers: tom.prince
Fixes: #5801

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@37824 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb