[SPARK-7401] [MLLIB] [PYSPARK] Vectorize dot product and sq_dist between SparseVector and DenseVector

Currently we iterate over indices which can be vectorized.

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #5946 from MechCoder/spark-7203 and squashes the following commits:

034d086 [MechCoder] Vectorize dot calculation for numpy arrays for ndim=2
bce2b07 [MechCoder] fix doctest
fcad0a3 [MechCoder] Remove type checks for list, pyarray etc
0ee5dd4 [MechCoder] Add tests and other isinstance changes
e5f1de0 [MechCoder] [SPARK-7401] Vectorize dot product and sq_dist