[SPARK-6612] [MLLIB] [PYSPARK] Python KMeans parity

The following items are added to Python kmeans:

kmeans - setEpsilon, setInitializationSteps
KMeansModel - computeCost, k

Author: Hrishikesh Subramonian <hrishikesh.subramonian@flytxt.com>

Closes #5647 from FlytxtRnD/newPyKmeansAPI and squashes the following commits:

b9e451b [Hrishikesh Subramonian] set seed to fixed value in doc test
5fd3ced [Hrishikesh Subramonian] doc test corrections
20b3c68 [Hrishikesh Subramonian] python 3 fixes
4d4e695 [Hrishikesh Subramonian] added arguments in python tests
21eb84c [Hrishikesh Subramonian] Python Kmeans - setEpsilon, setInitializationSteps, k and computeCost added.