fix several problems related to project build and test

[WeichenXu123]

What changes were proposed in this pull request?

• add maven goal <goal>test-jar</goal> so that mvn package will generate tests-jar.
• add test jar dependency for spark-core_2.11, spark-mllib_2.11, spark-mllib-local_2.11
• remove dependency for spark-graphx_2.11
• remove redundant test classes MLlibTestSparkContext, TestingUtils and TempDirectory which copied from spark test source.
• change all Suite class as SparkFunSuite subclass, instead of FunSuite. So that it will keep consistent with spark project.
• fix VLogisticRegressionSuite illegal toLocal usage.
• remove useless GridPartitioner in package ml.optim

  Usage

Use mvn package command, will generate two jars: spark-vlbfgs-1.0-SNAPSHOT.jar spark-vlbfgs-1.0-SNAPSHOT-tests.jar

Running the test suites, use the following command:

bin/spark-submit
   --driver-memory 3G
   --class org.scalatest.run #use scalatest.run to trigger the test suite running
   --jars ... #(add path to these jars: spark-core_2.11-2.1.0-SNAPSHOT-tests.jar, spark-mllib_2.11-2.1.0-SNAPSHOT-tests.jar, spark-mllib-local_2.11-2.1.0-SNAPSHOT-tests.jar, scalatest_2.11-2.2.6.jar, spark-vlbfgs-1.0-SNAPSHOT.jar)
   PATH/TO/spark-vlbfgs-1.0-SNAPSHOT-tests.jar
   org.apache.spark.ml.classification.VLogisticRegressionSuite  #the test suite class need to run