Deletes the configured OpenFlow controller address.

        This method is corresponding to the following ovs-vsctl command::

            $ ovs-vsctl del-controller <bridge>

def del_controller(self):
        """
        Deletes the configured OpenFlow controller address.

        This method is corresponding to the following ovs-vsctl command::

            $ ovs-vsctl del-controller <bridge>
        """
        command = ovs_vsctl.VSCtlCommand('del-controller', [self.br_name])
        self.run_command([command])