[SPARKR-118] SparkR build update to work with YARN

This patch adds support for building SparkR to run on YARN. This introduced two new variables `USE_YARN` and `SPARK_YARN_VERSION` that can be used to configure the build.

Most of the YARN dependencies are picked up from Cloudera's example POM for using Spark on YARN
http://maven-repository.com/artifact/org.apache.spark/spark-parent/1.1.0-cdh5.2.0/pom

Tested on a EC2 Hadoop 2.4.0 cluster.