[SPARK-1970] Update unit test in XORShiftRandomSuite to use ChiSquareTest from commons-math3

Updating the chisquare unit test in XORShiftRandomSuite to use the ChiSquareTest in commons-math3 instead of hardcoding the chisquare statistic for the desired confidence interval.

Author: Doris Xin <doris.s.xin@gmail.com>

Closes #1073 from dorx/math3Unit and squashes the following commits:

da0e891 [Doris Xin] remove math3 from common pom
9954143 [Doris Xin] merge master
c19948f [Doris Xin] Merge branch 'master' into math3Unit
8f84f19 [Doris Xin] [SPARK-1970] unit test in XORShiftRandomSuite
ffea61a [Doris Xin] SPARK-1939: Refactor takeSample method in RDD
1441977 [Doris Xin] SPARK-1939 Refactor takeSample method in RDD to use ScaSRS