[SPARK-2091][MLLIB] use numpy.dot instead of ndarray.dot

`ndarray.dot` is not available in numpy 1.4. This PR makes pyspark/mllib compatible with numpy 1.4.

Author: Xiangrui Meng <meng@databricks.com>

Closes #1035 from mengxr/numpy-1.4 and squashes the following commits:

7ad2f0c [Xiangrui Meng] use numpy.dot instead of ndarray.dot