Add YarnClientClusterScheduler and Backend.

With this scheduler, the user application is launched locally,
While the executor will be launched by YARN on remote nodes.

This enables spark-shell to run upon YARN.
Consolidated both mapPartitions related RDDs into a single MapPartitionsRDD.
Also changed the semantics of the index parameter in mapPartitionsWithIndex from the partition index of the output partition to the partition index in the current RDD.
Merge pull request #101 from colorant/yarn-client-scheduler

For SPARK-527, Support spark-shell when running on YARN

sync to trunk and resubmit here

In current YARN mode approaching, the application is run in the Application Master as a user program thus the whole spark context is on remote.

This approaching won't support application that involve local interaction and need to be run on where it is launched.

So In this pull request I have a YarnClientClusterScheduler and backend added.

With this scheduler, the user application is launched locally,While the executor will be launched by YARN on remote nodes with a thin AM which only launch the executor and monitor the Driver Actor status, so that when client app is done, it can finish the YARN Application as well.

This enables spark-shell to run upon YARN.

This also enable other Spark applications to have the spark context to run locally with a master-url "yarn-client". Thus e.g. SparkPi could have the result output locally on console instead of output in the log of the remote machine where AM is running on.

Docs also updated to show how to use this yarn-client mode.
Update tuning.md

Clarify when serializer is used based on recent user@ mailing list discussion.
Merge pull request #201 from rxin/mappartitions

Use the proper partition index in mapPartitionsWIthIndex

mapPartitionsWithIndex uses TaskContext.partitionId as the partition index. TaskContext.partitionId used to be identical to the partition index in a RDD. However, pull request #186 introduced a scenario (with partition pruning) that the two can be different. This pull request uses the right partition index in all mapPartitionsWithIndex related calls.

Also removed the extra MapPartitionsWIthContextRDD and put all the mapPartitions related functionality in MapPartitionsRDD.
Merge pull request #206 from ash211/patch-2

Update tuning.md

Clarify when serializer is used based on recent user@ mailing list discussion.