[SPARK-4435] [MLlib] [PySpark] improve classification

This PR add setThrehold() and clearThreshold() for LogisticRegressionModel and SVMModel, also support RDD of vector in LogisticRegressionModel.predict(), SVNModel.predict() and NaiveBayes.predict()
We use  `0 if prob < threshold else 1` in Scala, they should be consistant.