code: public static Message buildQueryReply(String leader) {
      QueryReply reply = QueryReply.newBuilder()
                                   .setLeader(leader)
                                   .build();
      return Message.newBuilder().setType(MessageType.QUERY_LEADER_REPLY)
                                 .setReply(reply)
                                 .build();
    }
docs: Creates a QUERY_REPLY message.
  
  @param leader the current leader in broadcasting phase.
  @return a protobuf message.