Support for SSL Client Authentication with MQTT

This as enhancement to add x509 client certification to the MQTT support. There should be an existing enhancement request per a conversation on the mailing list, http://grokbase.com/t/rabbitmq/rabbitmq-discuss/13bcejfs01/rabbitmq-mqtt-plugin-and-x509-client-certificate-authentication.

The code changes to the actual erlang code are small and follow a pattern similar to the STOMP adapter where the rabbit_mqtt_reader determines the login name from the socket and this is passed in to the initial state of rabbit_mqtt_processor. 

The majority of the changes in this pull request are mainly around the testing components and the build process. The configuration for running the tests utilizes either the file test/src/non_ssl.config or test/src/ssl.config to set up the parameters for testing, I refactored the support for running the Paho MQTT client tests and added an ant build file to make maintenance easier and do some SSL cert detection similar to the java amqp client project. The SSL cert testing will be conditionally run and the existing MQTT tests have not been changed.