def until_all_children_in_state(self, state, timeout=None):
        """Return a tornado Future; resolves when all clients are in specified state"""
        futures = [r.until_state(state, timeout=timeout)
                   for r in dict.values(self.children)]
        yield tornado.gen.multi(futures, quiet_exceptions=tornado.gen.TimeoutError)
Return a tornado Future; resolves when all clients are in specified state