as suggested by justinuang on #5601.

Author: Xiangrui Meng <meng@databricks.com>

Closes #5873 from mengxr/SPARK-7329 and squashes the following commits:

d08f9cf [Xiangrui Meng] simplify tests
b7a7b9b [Xiangrui Meng] simplify grid build

Author: Omede Firouz <ofirouz@palantir.com>
Author: Omede <omedefirouz@gmail.com>

Closes #5601 from oefirouz/paramgrid and squashes the following commits:

c9e2481 [Omede Firouz] Make test a doctest
9a8ce22 [Omede] Fix linter issues
8b8a6d2 [Omede Firouz] [SPARK-7022][PySpark][ML] Add ML.Tuning.ParamGridBuilder to PySpark