title: Transformer function not working for Seldon Core
body: <p>I'm testing Seldon Core and I have a sample model up and running with only <code>predict</code> function in my serving model <code>MyModel(object)</code>. 
  Now, I added <code>transform_input</code> function to preprocess input data before sending the input to the class. Again I deployed the model and it seemed working perfectly but I found that <code>transform_input</code> is not working or it's not used.
  I have found the <a href="https://docs.seldon.io/projects/seldon-core/en/latest/python/python_component.html" rel="nofollow noreferrer">doc</a> and <a href="https://github.com/SeldonIO/seldon-core/blob/master/examples/transformers/mean_transformer/MeanTransformer.py" rel="nofollow noreferrer">example</a> but it only shows to add the function <code>transform_input</code>. Am I missing something? </p>