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

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

Hmm. I said to change this to a more specific network error, but I was thinking there was a queue and a worker invoker to handled exceptions. So this does need to be a catch all Exception here.

That case should log.exception(e)  as well.