[SPARK-7431] [ML] [PYTHON] Made CrossValidatorModel call parent init in PySpark

Fixes bug with PySpark cvModel not having UID
Also made small PySpark fixes: Evaluator should inherit from Params.  MockModel should inherit from Model.

CC: mengxr

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #5968 from jkbradley/pyspark-cv-uid and squashes the following commits:

57f13cd [Joseph K. Bradley] Made CrossValidatorModel call parent init in PySpark

(cherry picked from commit 3038443e58)
Signed-off-by: Joseph K. Bradley <joseph@databricks.com>

python/pyspark/ml/pipeline.py

@@ -179,7 +179,7 @@ class PipelineModel(Model):
         return dataset
 
 
-class Evaluator(object):
+class Evaluator(Params):
     """
     Base class for evaluators that compute metrics from predictions.
     """

python/pyspark/ml/tests.py

@@ -34,7 +34,7 @@ from pyspark.tests import ReusedPySparkTestCase as PySparkTestCase
 from pyspark.sql import DataFrame
 from pyspark.ml.param import Param
 from pyspark.ml.param.shared import HasMaxIter, HasInputCol
-from pyspark.ml.pipeline import Transformer, Estimator, Pipeline
+from pyspark.ml.pipeline import Estimator, Model, Pipeline, Transformer
 
 
 class MockDataset(DataFrame):
@@ -77,7 +77,7 @@ class MockEstimator(Estimator):
         return model
 
 
-class MockModel(MockTransformer, Transformer):
+class MockModel(MockTransformer, Model):
 
     def __init__(self):
         super(MockModel, self).__init__()

python/pyspark/ml/tuning.py

@@ -236,6 +236,7 @@ class CrossValidatorModel(Model):
     """
 
     def __init__(self, bestModel):
+        super(CrossValidatorModel, self).__init__()
         #: best model from cross validation
         self.bestModel = bestModel