Fix PEP8 violations in examples/src/main/python.

Author: Reynold Xin <rxin@apache.org>

Closes #870 from rxin/examples-python-pep8 and squashes the following commits:

2829e84 [Reynold Xin] Fix PEP8 violations in examples/src/main/python.

(cherry picked from commit d79c2b28e17ec0b15198aaedd2e1f403d81f717e)
Signed-off-by: Reynold Xin <rxin@apache.org>