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

I tested this on both Hadoop 0.23 and Hadoop 2.0.2 on both secure and unsecure clusters.  This allows Spark on Yarn to get all the necessary tokens to start containers and run on a secure yarn cluster. It also forwards on the HDFS tokens to allow the containers to access HDFS files.  It currently only supports accessing HDFS file on the same cluster as being run.