Callback method that is fired for every message that comes in while we are in process_messages_loop.
        :param ch: channel message was sent on
        :param method: pika.Basic.Deliver
        :param properties: pika.BasicProperties
        :param body: str: payload of the message (picked WorkRequest)

def process_message(self, ch, method, properties, body):
        """
        Callback method that is fired for every message that comes in while we are in process_messages_loop.
        :param ch: channel message was sent on
        :param method: pika.Basic.Deliver
        :param properties: pika.BasicProperties
        :param body: str: payload of the message (picked WorkRequest)
        """
        self.work_request = pickle.loads(body)
        ch.basic_ack(delivery_tag=method.delivery_tag)
        self.process_work_request()