Client id set correctly for PUBLISH messages in the example server

For the publish message, the client id is retrieved from the packet itself. In the implementation of the examples servers, this was not the case, so I corrected that. I've also taken the liberty of adding a console.log to show that the clientid is set correctly (previsously it was 'undefined'). If possible, can we keep the console log, it's probably easier for beginning MQTT'ers like myself.
Note: The incoming messages publish were coming from a bridged mosquitto broker.