MQTT: WIP, re-organized disconnection handling, now keep track of connection status and reconnect accordingly.

This fixes bug with non-reconnecting to broker when having no published variables.

<?xml version='1.0' encoding='utf-8'?>
<OPCUAClient xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <AuthType/>
</OPCUAClient>