Gets the configured OpenFlow controller address.

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

            $ ovs-vsctl get-controller <bridge>

def get_controller(self):
        """
        Gets the configured OpenFlow controller address.

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

            $ ovs-vsctl get-controller <bridge>
        """
        command = ovs_vsctl.VSCtlCommand('get-controller', [self.br_name])
        self.run_command([command])
        result = command.result
        return result[0] if len(result) == 1 else result