title: module 'keras.backend' has no attribute 'tensorflow_backend'
body: <p>When I run my code where I am trying to use tensor flow as backend and I do the following:</p>
  <pre><code>import tensorflow
  KERAS_BACKEND=tensorflow
  import keras
  from keras import backend as K
  K.tensorflow_backend._get_available_gpus()
  </code></pre>
  <p>I get the following error:</p>
  <pre><code>K.tensorflow_backend._get_available_gpus()
  AttributeError: module 'keras.backend' has no attribute 'tensorflow_backend'
  </code></pre>
  <p>However, when I run the same piece of code on Jupyter notebook, it works and gives me the following output:</p>
  <pre><code>['/job:localhost/replica:0/task:0/device:GPU:0']
  </code></pre>
  <p>And this output means that tensowflow is installed. I don't get it why I get the above mentioned error when I run the same script through terminal. I am in the same environment in both cases. Insights would be appreciated.</p>