Implemented Exception propagation to the client
XD-443 Add MQTT Source

Parameters:

clientId (default 'xd.mqtt.client.id' from mqtt.properties)
topics (default 'xd.mqtt.test' from mqtt.properties)

See mqtt.properties for other properties such as broker
url.

To test:

Install RabbitMQ mqtt plugin

'mqtt | log'

Go to rabbit console, find queue 'mqtt-subscription-xd.mqtt.client.idqos1'
and publish a message to it.
XD-447 Add MQTT Sink

Parameters:

clientId (default 'xd.mqtt.client.id.snk' from mqtt.properties (+.snk))
topic (default 'xd.mqtt.test' from mqtt.properties)

See mqtt.properties for other properties such as broker
url.

To test:

Install RabbitMQ mqtt plugin

Create two streams:

'time --interval=5 | mqtt'
'mqtt | log'

Note: mqtt requires unique client ids; the mqtt source has been changed so
that its default clientId is now 'xd.mqtt.client.id.src' from mqtt.properties (+.src)).

XD-447 Add MQTT QOS and Retained Parameters

--qos=   --retained=
Fixing intermittent stest failures
Ditto for taps