title: Error in creating custom initializer using get_variable with Keras
body: <p>I created a custom initializer with Keras. Part of the code is: </p>
  
  <pre><code>def my_init(shape):
      P = tf.get_variable("P", shape=shape,    initializer = tf.contrib.layers.xavier_initializer())
      return P
  
  model = Sequential()
  model.add(Conv2D(32, kernel_size=(5, 5),strides=(1, 1), padding='same', input_shape = input_shape, kernel_initializer = my_init))
  model.add(MaxPooling2D(pool_size=(2, 2)))
  model.add(Conv2D(32, kernel_size=(1, 1) , strides=(1, 1) , padding='same' , kernel_initializer = my_init))
  </code></pre>
  
  <p>When "my_init" initializer is called for the second time in the convolution layer it throws this error: </p>
  
  <pre><code>Variable P already exists, disallowed. Did you mean to set reuse=True in VarScope? Originally defined at:
  </code></pre>
  
  <p>It is not allowing to reuse the variable P. Is there any way to create a new variable in each call?</p>