Created by: lcy-seso

• This PR https://github.com/PaddlePaddle/Paddle/pull/2288 changes the way v2 APIs parse the network configuration. But currently, beam search cannot be parsed correctly. It causes bugs to machine translation in PaddleBook.

• This PR https://github.com/PaddlePaddle/Paddle/pull/2384 fix the training process but hasn't fixed bugs in the generation.

• I change is_generating=True in this line https://github.com/PaddlePaddle/book/blob/develop/08.machine_translation/train.py#L129, the error information go as follows

I0605 18:50:24.263185 18007 Util.cpp:166] commandline:  --use_gpu=False --trainer_count=1
F0605 18:50:46.687893 18007 NeuralNetwork.h:94] Check failed: it != layerMap_.end() Unknown layer __decoder_group_eos_layer__@decoder_group
*** Check failure stack trace: ***
    @     0x7f7019fed7bd  google::LogMessage::Fail()
    @     0x7f7019ff126c  google::LogMessage::SendToLog()
    @     0x7f7019fed2e3  google::LogMessage::Flush()
    @     0x7f7019ff277e  google::LogMessageFatal::~LogMessageFatal()
    @     0x7f7019c2afef  paddle::NeuralNetwork::getLayer()
    @     0x7f7019c3932c  paddle::RecurrentGradientMachine::resizeOrCreateFrames()
    @     0x7f7019c3873b  paddle::RecurrentGradientMachine::init()
    @     0x7f7019bd3be9  paddle::RecurrentLayerGroup::initSubNetwork()
    @     0x7f7019c285c5  paddle::NeuralNetwork::init()
    @     0x7f7019c52bde  paddle::GradientMachine::create()
    @     0x7f7019fc10cc  GradientMachine::createFromPaddleModelPtr()
    @     0x7f7019fc120d  GradientMachine::createByConfigProtoStr()
    @     0x7f7019ab07d5  _wrap_GradientMachine_createByConfigProtoStr__SWIG_0
    @     0x7f7019ab0e10  _wrap_GradientMachine_createByConfigProtoStr
    @     0x7f7021f513a3  PyEval_EvalFrameEx
    @     0x7f7021f53130  PyEval_EvalCodeEx
    @     0x7f7021f514a1  PyEval_EvalFrameEx
    @     0x7f7021f53130  PyEval_EvalCodeEx
    @     0x7f7021f514a1  PyEval_EvalFrameEx
    @     0x7f7021f53130  PyEval_EvalCodeEx
    @     0x7f7021edf27d  function_call
    @     0x7f7021eb70f3  PyObject_Call
    @     0x7f7021ec9f7f  instancemethod_call
    @     0x7f7021eb70f3  PyObject_Call
    @     0x7f7021f0d80e  slot_tp_init
    @     0x7f7021f0c478  type_call
    @     0x7f7021eb70f3  PyObject_Call
    @     0x7f7021f50887  PyEval_EvalFrameEx
    @     0x7f7021f53130  PyEval_EvalCodeEx
    @     0x7f7021f514a1  PyEval_EvalFrameEx
    @     0x7f7021f51c56  PyEval_EvalFrameEx
    @     0x7f7021f53130  PyEval_EvalCodeEx

Besides eos_layer, several other layers are not created in generation.