Removed unused return value in SparkContext.runJob
Merge pull request #144 from liancheng/runjob-clean

Removed unused return value in SparkContext.runJob

Return type of this `runJob` version is `Unit`:

    def runJob[T, U: ClassManifest](
        rdd: RDD[T],
        func: (TaskContext, Iterator[T]) => U,
        partitions: Seq[Int],
        allowLocal: Boolean,
        resultHandler: (Int, U) => Unit) {
        ...
    }

It's obviously unnecessary to "return" `result`.
Add Spark multi-user support for standalone mode and Mesos
Merge pull request #23 from jerryshao/multi-user

Add Spark multi-user support for standalone mode and Mesos

This PR add multi-user support for Spark both standalone mode and Mesos (coarse and fine grained ) mode, user can specify the user name who submit app through environment variable `SPARK_USER` or use default one. Executor will communicate with Hadoop using  specified user name.

Also I fixed one bug in JobLogger when different user wrote job log to specified folder which has no right file  permission.

I separate previous [PR750](https://github.com/mesos/spark/pull/750) into two PRs, in this PR I only solve multi-user support problem. I will try to solve security auth problem in subsequent PR because security auth is a complicated problem especially for Shark Server like long-run app (both Kerberos TGT and HDFS delegation token should be renewed or re-created through app's run time).