Sets a Qos rule and creates Queues on the given port.

def set_qos(self, port_name, type='linux-htb', max_rate=None, queues=None):
        """
        Sets a Qos rule and creates Queues on the given port.
        """
        queues = queues if queues else []
        command_qos = ovs_vsctl.VSCtlCommand(
            'set-qos',
            [port_name, type, max_rate])
        command_queue = ovs_vsctl.VSCtlCommand(
            'set-queue',
            [port_name, queues])
        self.run_command([command_qos, command_queue])
        if command_qos.result and command_queue.result:
            return command_qos.result + command_queue.result
        return None