SPARK-1793 - Heavily duplicated test setup code in SVMSuite

Summary:
Refactor the code to remove the repeated initialization of
test/validation RDDs in every test.

Test Plan:
Unit tests cover this code and pass with this update.

Reviewers:

CC:

Conflicts:
	mllib/src/test/scala/org/apache/spark/mllib/classification/SVMSuite.scala