Currently when we run tests, this connects to OFTC and tries to use
the opendevstatus nick as it is the default. Replace this with a
random username. Also override the channels list, so it only joins
Limnoria was already using a non-conflicting name, but switch it to a
random one for consistency and possible parallel running. This also
already only joins #opendev-sandbox.
Change-Id: I860b0f1ed4f99140dda0f4d41025f0b5fb844115
4ffcc89c8a