Clears values from 'column' in 'record' in 'table'.

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

            $ ovs-vsctl clear TBL REC COL

def clear_db_attribute(self, table, record, column):
        """
        Clears values from 'column' in 'record' in 'table'.

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

            $ ovs-vsctl clear TBL REC COL
        """
        command = ovs_vsctl.VSCtlCommand('clear', (table, record, column))
        self.run_command([command])