[SPARK-2871] [PySpark] add zipWithIndex() and zipWithUniqueId()

RDD.zipWithIndex()

        Zips this RDD with its element indices.

        The ordering is first based on the partition index and then the
        ordering of items within each partition. So the first item in
        the first partition gets index 0, and the last item in the last
        partition receives the largest index.

        This method needs to trigger a spark job when this RDD contains
        more than one partitions.

        >>> sc.parallelize(range(4), 2).zipWithIndex().collect()
        [(0, 0), (1, 1), (2, 2), (3, 3)]

RDD.zipWithUniqueId()

        Zips this RDD with generated unique Long ids.

        Items in the kth partition will get ids k, n+k, 2*n+k, ..., where
        n is the number of partitions. So there may exist gaps, but this
        method won't trigger a spark job, which is different from
        L{zipWithIndex}

        >>> sc.parallelize(range(4), 2).zipWithUniqueId().collect()
        [(0, 0), (2, 1), (1, 2), (3, 3)]

Author: Davies Liu <davies.liu@gmail.com>

Closes #2092 from davies/zipWith and squashes the following commits:

cebe5bf [Davies Liu] improve test cases, reverse the order of index
0d2a128 [Davies Liu] add zipWithIndex() and zipWithUniqueId()

(cherry picked from commit fb0db772421b6902b80137bf769db3b418ab2ccf)
Signed-off-by: Josh Rosen <joshrosen@apache.org>
[SPARK-2495][MLLIB] make KMeans constructor public

to re-construct k-means models freeman-lab

Author: Xiangrui Meng <meng@databricks.com>

Closes #2112 from mengxr/public-constructors and squashes the following commits:

18d53a9 [Xiangrui Meng] make KMeans constructor public

(cherry picked from commit 220f413686ae922bd11776576bf37610cce92c23)
Signed-off-by: Xiangrui Meng <meng@databricks.com>
SPARK-2798 [BUILD] Correct several small errors in Flume module pom.xml files

(EDIT) Since the scalatest issue was since resolved, this is now about a few small problems in the Flume Sink `pom.xml`

- `scalatest` is not declared as a test-scope dependency
- Its Avro version doesn't match the rest of the build
- Its Flume version is not synced with the other Flume module
- The other Flume module declares its dependency on Flume Sink slightly incorrectly, hard-coding the Scala 2.10 version
- It depends on Scala Lang directly, which it shouldn't

Author: Sean Owen <sowen@cloudera.com>

Closes #1726 from srowen/SPARK-2798 and squashes the following commits:

a46e2c6 [Sean Owen] scalatest to test scope, harmonize Avro and Flume versions, remove direct Scala dependency, fix '2.10' in Flume dependency

(cherry picked from commit cd30db566a327ddf63cd242c758e46ce2d9479df)
Signed-off-by: Tathagata Das <tathagata.das1565@gmail.com>
[FIX] fix error message in sendMessageReliably

rxin

Author: Xiangrui Meng <meng@databricks.com>

Closes #2120 from mengxr/sendMessageReliably and squashes the following commits:

b14400c [Xiangrui Meng] fix error message in sendMessageReliably

(cherry picked from commit fd8ace2d9a796f69ce34ad202907008cd6e4d274)
Signed-off-by: Josh Rosen <joshrosen@apache.org>
Fixed a typo in docs/running-on-mesos.md

It should be `spark-env.sh` rather than `spark.env.sh`.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2119 from liancheng/fix-mesos-doc and squashes the following commits:

f360548 [Cheng Lian] Fixed a typo in docs/running-on-mesos.md

(cherry picked from commit 805fec845b7aa8b4763e3e0e34bec6c3872469f4)
Signed-off-by: Josh Rosen <joshrosen@apache.org>