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

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

Something in this class is resulting in an attempt to connect to the server setup in the systems /etc/rhsm/rhsm.conf

If possible, it shouldn't need to read the config file. It should also avoid attempting to make connections to real systems. [1]

[1] We are likely violating that in other tests, but the goal is to avoid it.