Add support for Spark on Yarn on a secure Hadoop cluster
upmerge with latest mesos/spark master and fix hbase compile with hadoop2-yarn profile
Rework from pull request. Removed --user option from Spark on Yarn Client, made the user of JAVA_HOME environment
variable conditional on if its set, and created addCredentials in each of the SparkHadoopUtil classes
to only add the credentials when the profile is hadoop2-yarn.
Merge pull request #655 from tgravescs/master

Add support for running Spark on Yarn on a secure Hadoop Cluster