test-modem-call: use "multiparty" property
test-modem-call: use "multiparty" property

matthewvogt/telepathy-ring,jpoutiai/telepathy-ring,freedesktop-unofficial-mirror/telepathy__telepathy-ring,matthewvogt/telepathy-ring,freedesktop-unofficial-mirror/telepathy__telepathy-ring,matthewvogt/telepathy-ring,maemo-foss/meego-cellular-telepathy-ring,maemo-foss/meego-cellular-telepathy-ring,maemo-foss/meego-cellular-telepathy-ring,freedesktop-unofficial-mirror/telepathy__telepathy-ring,jpoutiai/telepathy-ring,jpoutiai/telepathy-ring