def ask_children_for_capacities(self, ctxt):
        child_cells = self.state_manager.get_child_cells()
        for child_cell in child_cells:
            message = _TargetedMessage(self, ctxt, 'announce_capacities',
                                        dict(), 'down', child_cell)
            message.process()
Tell child cells to send us capacities.  This is typically
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/cells/messaging.py/MessageRunner.ask_children_for_capacities