[SPARK-3417] Use new-style classes in PySpark

Tiny PR making SQLContext a new-style class.  This allows various type logic to work more effectively

```Python
In [1]: import pyspark

In [2]: pyspark.sql.SQLContext.mro()
Out[2]: [pyspark.sql.SQLContext, object]
```

Author: Matthew Rocklin <mrocklin@gmail.com>

Closes apache#2288 from mrocklin/sqlcontext-new-style-class and squashes the following commits:

4aadab6 [Matthew Rocklin] update other old-style classes
a2dc02f [Matthew Rocklin] pyspark.sql.SQLContext is new-style class

python/pyspark/mllib/random.py

@@ -28,7 +28,7 @@
 __all__ = ['RandomRDDs', ]
 
 
-class RandomRDDs:
+class RandomRDDs(object):
     """
     Generator methods for creating RDDs comprised of i.i.d samples from
     some distribution.

python/pyspark/mllib/util.py

@@ -25,7 +25,7 @@
 from pyspark.serializers import NoOpSerializer
 
 
-class MLUtils:
+class MLUtils(object):
 
     """
     Helper methods to load, save and pre-process data used in MLlib.

python/pyspark/sql.py

@@ -899,7 +899,7 @@ def __reduce__(self):
     return Row
 
 
-class SQLContext:
+class SQLContext(object):
 
     """Main entry point for Spark SQL functionality.
 

python/pyspark/storagelevel.py

@@ -18,7 +18,7 @@
 __all__ = ["StorageLevel"]
 
 
-class StorageLevel:
+class StorageLevel(object):
 
     """
     Flags for controlling the storage of an RDD. Each StorageLevel records whether to use memory,