[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
[SPARK-4378][MLLIB] make ALS more Java-friendly

Add Java-friendly version of `run` and `predict`, and use bulk prediction in Java unit tests. The user guide update will come later (though we may not save many lines of code there). srowen

Author: Xiangrui Meng <meng@databricks.com>

Closes #3240 from mengxr/SPARK-4378 and squashes the following commits:

6581503 [Xiangrui Meng] check number of predictions
6c8bbd1 [Xiangrui Meng] make ALS more Java-friendly
[HOT FIX] make-distribution.sh fails if Yarn shuffle jar DNE

This is introduced in #3147 and is failing builds without the `-Pyarn` profile.

Author: Andrew Or <andrew@databricks.com>

Closes #3250 from andrewor14/fix-yarn-shuffle-build and squashes the following commits:

42b3d37 [Andrew Or] Do not fail fast if Yarn shuffle jar does not exist
[SPARK-4326] fix unidoc

There are two issues:

1. specifying guava 11.0.2 will cause hashInt not found in unidoc (any reason to force the version here?)
2. unidoc doesn't recognize static class defined in a base class

aarondav srowen vanzin

Author: Xiangrui Meng <meng@databricks.com>

Closes #3253 from mengxr/SPARK-4326 and squashes the following commits:

53967bf [Xiangrui Meng] fix unidoc