[SPARK-4821] [mllib] [python] [docs] Fix for pyspark.mllib.rand doc

+ small doc edit
+ include edit to make IntelliJ happy

CC: @davies  @mengxr

Note to @davies  -- this does not fix the "WARNING: Literal block expected; none found." warnings since that seems to involve spacing which IntelliJ does not like.  (Those warnings occur when generating the Python docs.)
It could be fixed by 
```
diff --git a/python/pyspark/mllib/__init__.py b/python/pyspark/mllib/__init__.py
index 5030a65..cba540a 100644
--- a/python/pyspark/mllib/__init__.py
+++ b/python/pyspark/mllib/__init__.py
@@ -32,7 +32,7 @@ import sys
 import rand as random
 random.__name__ = 'random'
 random.RandomRDDs.__module__ = __name__ + '.random'

+sys.modules[__name__ + '.random'] = random

 class RandomModuleHook(object):
     """
```