Keras multi gpu duplicate model names

repro.py

from keras.models import Model
from keras.layers import Input, Add
from keras.utils import multi_gpu_model

m_in = Input( shape=(1,) )
m_out1 = Add()([m_in,m_in])
m_out2 = m_in
m = Model( m_in, [m_out1,m_out2] )

x = Input( shape=(1,) )

compoundModel = Model( x, m( x ) )
compoundModel = multi_gpu_model( compoundModel ,2)
#RuntimeError: ('The name "model_1" is used 2 times in the model. All layer names should be unique. Layer names: ', 
#['input_2', 'lambda_1', 'lambda_2', 'model_2', 'model_1', 'model_1'])

training_utils_possible_fix.py

  # Merge outputs on CPU.
  with tf.device('/cpu:0'):
      merged = []
      for n,(name, outputs) in enumerate(zip(model.output_names, all_outputs)):
          merged.append(concatenate(outputs,
                                    axis=0, name=name+'_gpu_'+str(n)))
        

Would you please make a pr? This is useful to me.