part of fd.o #20909: McdDispatcher: work out the dispatch operation path, but don't use it yet
part of fd.o #20909: McdDispatcher: work out the dispatch operation path, but don't use it yet

This will be passed to ObserveChannels when we break API.

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control