public void reply(Reply reply) {
        ReplyHandler handler = reply.popHandler();
        handler.handleReply(reply);
    }
Sends a reply to a message. The reply will propagate back to the original sender, preferring the same route as it
used to reach the destination.

@param reply The reply, created from the message this is a reply to.
messagebus/src/main/java/com/yahoo/messagebus/DestinationSession.java