[SPARK-4708][MLLib] Make k-mean runs two/three times faster with dense/sparse sample

Note that the usage of `breezeSquaredDistance` in
`org.apache.spark.mllib.util.MLUtils.fastSquaredDistance`
is in the critical path, and `breezeSquaredDistance` is slow.
We should replace it with our own implementation.

Here is the benchmark against mnist8m dataset.

Before
DenseVector: 70.04secs
SparseVector: 59.05secs

With this PR
DenseVector: 30.58secs
SparseVector: 21.14secs

Author: DB Tsai <dbtsai@alpinenow.com>

Closes #3565 from dbtsai/kmean and squashes the following commits:

08bc068 [DB Tsai] restyle
de24662 [DB Tsai] address feedback
b185a77 [DB Tsai] cleanup
4554ddd [DB Tsai] first commit

(cherry picked from commit 7fc49ed91168999d24ae7b4cc46fbb4ec87febc1)
Signed-off-by: Xiangrui Meng <meng@databricks.com>