'If the node identified by given ID is dead, return ``True``. If it\'s
alive or unknown, return ``False``.
@param unicode instance_id: Node identifier.
@return: Whether instance is known to be dead.'

def is_known_dead_instance(self, instance_id):

    if (self._live_instances is None):
        return False
    return (instance_id not in self._live_instances)
