Init the connection to the MQTT server.

def init(self):
        """Init the connection to the MQTT server."""
        if not self.export_enable:
            return None
        try:
            client = paho.Client(client_id='glances_' + self.hostname,
                                 clean_session=False)
            client.username_pw_set(username=self.user,
                                   password=self.password)
            if self.tls:
                client.tls_set(certs.where())
            client.connect(host=self.host,
                           port=self.port)
            client.loop_start()
            return client
        except Exception as e:
            logger.critical("Connection to MQTT server failed : %s " % e)
            return None