Update mllib data gen
Update mllib data gen

1. Keep seed in range `[0, 2*32)`.
2. Generate exactly `numExamples` examples.
3. Do not dedup in generating ratings.

Author: Xiangrui Meng <meng@databricks.com>

Closes #60 from mengxr/py-mllib-data-gen and squashes the following commits:

cc9c67d [Xiangrui Meng] mix with hash(str(..))
7c878b7 [Xiangrui Meng] update py-mllib-data-gen

arijitt/spark-perf,mengxr/spark-perf,Altiscale/spark-perf,jkbradley/spark-perf,databricks/spark-perf,XiaoqingWang/spark-perf,nchammas/spark-perf,feynmanliang/spark-perf,zsxwing/spark-perf,jkbradley/spark-perf,zsxwing/spark-perf,Altiscale/spark-perf,feynmanliang/spark-perf,XiaoqingWang/spark-perf,nchammas/spark-perf,mengxr/spark-perf,arijitt/spark-perf,databricks/spark-perf