[SPARK-4330][Doc] Link to proper URL for YARN overview

In running-on-yarn.md, a link to YARN overview is here.
But the URL is to YARN alpha's.
It should be stable's.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #3196 from sarutak/SPARK-4330 and squashes the following commits:

30baa21 [Kousuke Saruta] Fixed running-on-yarn.md to point proper URL for YARN

(cherry picked from commit 3c07b8f08240bafcdff5d174989fb433f4bc80b6)
Signed-off-by: Matei Zaharia <matei@databricks.com>
[SPARK-4324] [PySpark] [MLlib] support numpy.array for all MLlib API

This PR check all of the existing Python MLlib API to make sure that numpy.array is supported as Vector (also RDD of numpy.array).

It also improve some docstring and doctest.

cc mateiz mengxr

Author: Davies Liu <davies@databricks.com>

Closes #3189 from davies/numpy and squashes the following commits:

d5057c4 [Davies Liu] fix tests
6987611 [Davies Liu] support numpy.array for all MLlib API

(cherry picked from commit 65083e93ddd552b7d3e4eb09f87c091ef2ae83a2)
Signed-off-by: Xiangrui Meng <meng@databricks.com>
[SPARK-4307] Initialize FileDescriptor lazily in FileRegion.

Netty's DefaultFileRegion requires a FileDescriptor in its constructor, which means we need to have a opened file handle. In super large workloads, this could lead to too many open files due to the way these file descriptors are cleaned. This pull request creates a new LazyFileRegion that initializes the FileDescriptor when we are sending data for the first time.

Author: Reynold Xin <rxin@databricks.com>
Author: Reynold Xin <rxin@apache.org>

Closes #3172 from rxin/lazyFD and squashes the following commits:

0bdcdc6 [Reynold Xin] Added reference to Netty's DefaultFileRegion
d4564ae [Reynold Xin] Added SparkConf to the ctor argument of IndexShuffleBlockManager.
6ed369e [Reynold Xin] Code review feedback.
04cddc8 [Reynold Xin] [SPARK-4307] Initialize FileDescriptor lazily in FileRegion.

(cherry picked from commit ef29a9a9aa85468869eb67ca67b66c65f508d0ee)
Signed-off-by: Aaron Davidson <aaron@databricks.com>