I compared PySpark DataFrameReader/Writer against Scala ones. `Option` function is missing in both reader and writer, but the rest seems to all match.

I added `Option` to reader and writer and updated the `pyspark-sql` test.

Author: Cheolsoo Park <cheolsoop@netflix.com>

Closes #7078 from piaozhexiu/SPARK-8355 and squashes the following commits:

c63d419 [Cheolsoo Park] Fix version
524e0aa [Cheolsoo Park] Add option function to df reader and writer