groups.py: factor out parse_roster_change_request()
groups.py: factor out parse_roster_change_request()

https://bugs.freedesktop.org/show_bug.cgi?id=45982

mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble