Added make_svhn_pytables.py to whitelist_docstrings

[chg] Whitelisted make_svhn_pytables.py to skip docstrings testing on Travis CI.
[chg] Added check to ensure 'PYLEARN2_DATA_PATH' is defined as an environment
      variable before conversion to pytables.

Author: sandeepkbhat

pylearn2/scripts/datasets/make_svhn_pytables.py

@@ -7,9 +7,8 @@
 import os
 from pylearn2.datasets.svhn import SVHN
 from pylearn2.utils.string_utils import preprocess
-from pylearn2.testing.skip import skip_if_no_data
 
-skip_if_no_data() # Checking if PYLEARN2_DATA_PATH exists
+assert 'PYLEARN2_DATA_PATH' in os.environ, "PYLEARN2_DATA_PATH not defined"
 
 orig_path = preprocess('${PYLEARN2_DATA_PATH}/SVHN/format2/')