Fix MUC login: Support tuple & add username

In order to enable MUC for XMPP I needed to tweak `callback_connect`:

- `logging` fails if we have to deal with a tuple
  The values need to be accessed by index if we have a tuple
- add parameter `username` in `join_room` with a name

Otherwise the connection can not be established.
Merge pull request #189 from ctrabold/support_xmpp_muc

Fix MUC login: Support tuple & add username