Instead of disabling all python style check, we should enable PEP8. So, this PR just comments out the part installing pylint.

Author: Yin Huai <yhuai@databricks.com>

Closes #7704 from yhuai/SPARK-9385 and squashes the following commits:

0056359 [Yin Huai] Enable PEP8 but disable installing pylint.