conversation_module: retry to sync if first connection fails

If first connection fails and presence is not tracked, the
conversation will not sync until the receiver restarts its jami,
causing the conversation to be stuck a very long time even if
peer is online and can sync.
In this patch, if we receives a trust request, we retry to sync
(this will be the case because the sender will re-send a trust
request to the contact who is still detected as an invited member)

GitLab: #922
Change-Id: I8866ceda98d50b0ddd2ea5402ef34f067f560e97