Use the existing method that grossly sets attributes on other objects instead of duplicating that grossness.

Also make MockConnection an actual SSHService so that it works with this setService method.


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/conch-channel-addresses-5999@43523 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb