'Called by the cell scheduler to tell a child cell to build
instance(s).'

def build_instances(self, ctxt, target_cell, build_inst_kwargs):

    method_kwargs = dict(build_inst_kwargs=build_inst_kwargs)
    message = _TargetedMessage(self, ctxt, 'build_instances', method_kwargs, 'down', target_cell)
    message.process()
