Add tensorflow-datasets package

This package do not include the datasets. It is merely a
nice interface to load dataset from GCS.

BUG=158329670

Author: rosbo

Dockerfile

@@ -438,6 +438,7 @@ RUN pip install flashtext && \
     # papermill can replace nbconvert for executing notebooks
     pip install papermill && \
     pip install cloud-tpu-client && \
+    pip install tensorflow-datasets && \
     /tmp/clean-layer.sh
 
 # Tesseract and some associated utility packages

tests/test_imports.py

@@ -6,3 +6,4 @@ def test_basic(self):
         import bq_helper
         import cleverhans
         import tensorflow_gcs_config
+        import tensorflow_datasets