add multiple sessions tests to muc suite
fix exiting from multisession and reenable all tests
Removed unnecessary comments; fixed naming
Renamed is_*_message_correct to assert_is_*_message_correct
Extracted enter_room/3 from multiple_sessions_enter_room_helper/4
Changed enter_room/3 calls to lists:foldl
Renamed multiple_sessions_enter_room_helper/4 to populate_room_with_users/2
Merge pull request #66 from pianiel/muc_multi_session

Muc multi session