[SPARK-4373][MLLIB] fix MLlib maven tests

We want to make sure there is at most one spark context inside the same jvm. JoshRosen

Author: Xiangrui Meng <meng@databricks.com>

Closes #3235 from mengxr/SPARK-4373 and squashes the following commits:

6574b69 [Xiangrui Meng] rename LocalSparkContext to MLlibTestSparkContext
913d48d [Xiangrui Meng] make sure there is at most one spark context inside the same jvm
[SPARK-4370] [Core] Limit number of Netty cores based on executor size

Author: Aaron Davidson <aaron@databricks.com>

Closes #3155 from aarondav/conf and squashes the following commits:

7045e77 [Aaron Davidson] Add mesos comment
4770f6e [Aaron Davidson] [SPARK-4370] [Core] Limit number of Netty cores based on executor size
[SPARK-4256] Make Binary Evaluation Metrics functions defined in cases where there ar...

...e 0 positive or 0 negative examples.

Author: Andrew Bullen <andrew.bullen@workday.com>

Closes #3118 from abull/master and squashes the following commits:

c2bf2b1 [Andrew Bullen] [SPARK-4256] Update Code formatting for BinaryClassificationMetricsSpec
36b0533 [Andrew Bullen] [SYMAN-4256] Extract BinaryClassificationMetricsSuite assertions into private method
4d2f79a [Andrew Bullen] [SPARK-4256] Refactor classification metrics tests - extract comparison functions in test
f411e70 [Andrew Bullen] [SPARK-4256] Define precision as 1.0 when there are no positive examples; update code formatting per pull request comments
d9a09ef [Andrew Bullen] Make Binary Evaluation Metrics functions defined in cases where there are 0 positive or 0 negative examples.
[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