Couple enhancements.

A random long number is appended to the test channel names,
so that each run potentially handles new test channels instead of always the same,
in order to avoid some tests being messed up due to previously existing test channels being
used inadvertidly by someone.

Added couple feeback enhancements as well.

Renamed test_user_channel_closed to test_user_channel_authorized to
reflect the XMPP_XEP.