[SPARK-2172] PySpark cannot import mllib modules in YARN-client mode

Include pyspark/mllib python sources as resources in the mllib.jar.
This way they will be included in the final assembly

Author: Szul, Piotr <Piotr.Szul@csiro.au>

Closes #1223 from piotrszul/branch-1.0 and squashes the following commits:

69d5174 [Szul, Piotr] Removed unsed resource directory src/main/resource from mllib pom
f8c52a0 [Szul, Piotr] [SPARK-2172] PySpark cannot import mllib modules in YARN-client mode Include pyspark/mllib python sources as resources in the jar