follow pep8 None should be compared using is or is not

http://legacy.python.org/dev/peps/pep-0008/
## Programming Recommendations
- Comparisons to singletons like None should always be done with is or is not, never the equality operators.

Author: Ken Takagiwa <ken@Kens-MacBook-Pro.local>

Closes #1422 from giwa/apache_master and squashes the following commits:

7b361f3 [Ken Takagiwa] follow pep8 None should be checked using is or is not
[SPARK-2314][SQL] Override collect and take in JavaSchemaRDD, forwarding to SchemaRDD implementations.

Author: Aaron Staple <aaron.staple@gmail.com>

Closes #1421 from staple/SPARK-2314 and squashes the following commits:

73e04dc [Aaron Staple] [SPARK-2314] Override collect and take in JavaSchemaRDD, forwarding to SchemaRDD implementations.