Summary: updates for DecisionTree tests.

PerfTest.scala
* Added doubleOptionValue()

MLAlgorithmTests.scala
* DecisionTreeTests: abstract class extending RegressionAndClassificationTests, to be combined after the MLlib API update.
* DecisionTreeTest

DataGenerator.scala
* generateDecisionTreeLabeledPoints, with helper methods:
** randomBalancedDecisionTree
** randomBalancedDecisionTreeHelper
** ClassLabelPairGenerator
** RealLabelPairGenerator
** FeaturesGenerator
Merged DecisionTree updates with other tests.
Updated config.py.template for decision tree test
Merge pull request #1 from jkbradley/decisiontree

DecisionTree tests for spark-perf