Fix #655 - Added a DisconnectHandler to xmppclient when using ssl

When the xmpp connexion is falling we have an infinite loop on main
loop.
So by adding a DisconnectHandler, I can reset the loop_status and avoid
infinite loop.

Note : this only occurs when using a C2S SSL connexion.
Merge branch 'add-xmpp-disconnecthandler' of https://github.com/CyrilPeponnet/Archipel into pr-674