[SPARK-4348] [PySpark] [MLlib] rename random.py to rand.py

This PR rename random.py to rand.py to avoid the side affects of conflict with random module, but still keep the same interface as before.

```
>>> from pyspark.mllib.random import RandomRDDs
```

```
$ pydoc pyspark.mllib.random
Help on module random in pyspark.mllib:
NAME
    random - Python package for random data generation.

FILE
    /Users/davies/work/spark/python/pyspark/mllib/rand.py

CLASSES
    __builtin__.object
        pyspark.mllib.random.RandomRDDs

    class RandomRDDs(__builtin__.object)
     |  Generator methods for creating RDDs comprised of i.i.d samples from
     |  some distribution.
     |
     |  Static methods defined here:
     |
     |  normalRDD(sc, size, numPartitions=None, seed=None)
```

cc mengxr

reference link: http://xion.org.pl/2012/05/06/hacking-python-imports/

Author: Davies Liu <davies@databricks.com>

Closes #3216 from davies/random and squashes the following commits:

7ac4e8b [Davies Liu] rename random.py to rand.py

1 files changed, 34 insertions, 0 deletions

diff --git a/python/pyspark/mllib/__init__.py b/python/pyspark/mllib/__init__.py
index 4149f54931..5030a655fc 100644
--- a/python/pyspark/mllib/__init__.py
+++ b/python/pyspark/mllib/__init__.py
@@ -24,3 +24,37 @@ Python bindings for MLlib.
 import numpy
 if numpy.version.version < '1.4':
     raise Exception("MLlib requires NumPy 1.4+")
+
+__all__ = ['classification', 'clustering', 'feature', 'linalg', 'random',
+           'recommendation', 'regression', 'stat', 'tree', 'util']
+
+import sys
+import rand as random
+random.__name__ = 'random'
+random.RandomRDDs.__module__ = __name__ + '.random'
+
+
+class RandomModuleHook(object):
+    """
+    Hook to import pyspark.mllib.random
+    """
+    fullname = __name__ + '.random'
+
+    def find_module(self, name, path=None):
+        # skip all other modules
+        if not name.startswith(self.fullname):
+            return
+        return self
+
+    def load_module(self, name):
+        if name == self.fullname:
+            return random
+
+        cname = name.rsplit('.', 1)[-1]
+        try:
+            return getattr(random, cname)
+        except AttributeError:
+            raise ImportError
+
+
+sys.meta_path.append(RandomModuleHook())