SPARK-1051. On YARN, executors don't doAs submitting user

This reopens https://github.com/apache/incubator-spark/pull/538 against the new repo

Author: Sandy Ryza <sandy@cloudera.com>

Closes #29 from sryza/sandy-spark-1051 and squashes the following commits:

708ce49 [Sandy Ryza] SPARK-1051. doAs submitting user in YARN
SPARK-1151: Update dev merge script to use spark.git instead of incubator-spark

Author: Thomas Graves <tgraves@apache.org>

Closes #47 from tgravescs/fix_merge_script and squashes the following commits:

8209ab1 [Thomas Graves] Update dev merge script to use spark.git instead of incubator-spark
Added CPU logging
Added network logging
Fixed sign issues, changed to Scala files
Added logging to worker and fixed overflow
Fixed overflow issue in parsing
Added time to all log messages and removed commas for easier parsing
Add logging for task start/finish millis
Increase logging frequency
More comma removal
Check for non-zero elapsed CPU time
Check for non-zero time delta
Added new CPU utilization computation metric
Check for non-zero elapsed time
Much more extensive CPU logging
Fixed int/double division issue
Fixed typo and added idle time logging
Added parsing of diskstats file
Fixing compile errors