1070585: GUI no longer locks on connection test. Adds cancel button.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1070585

Hmm, I'm unsure what to expect mocking threading.Thread. 

That makes the Thread class a Mock, so the code that creates a Thread is calling a Mock(target=blah, args=(blah,etc)), so mock_thread is the Mock() class returned by calling init of the Mock you pass in.

That Mock (thread_mock) ends up with the thread init in it's call list. But the init is called with a reference
to a set of args, name, and target. (ie, nothing is actually called with the args of 'example.com' etc, but
the thread init does get a method argument called "args" that is the tuple ('example.com,...etc)


Check out for a different approach, alikins/proxy_config_write_fix_mock
So mock_thread (