groups.py: test RenameGroup()
groups.py: test RenameGroup()

This has been started as a regression test for fdo#45982 which turned to be a
tp-glib bug. So we shouldn't merge this commit to master until we depend on a
fixed tp-glib.

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