[SPARK-3674] YARN support in Spark EC2

This corresponds to https://github.com/mesos/spark-ec2/pull/116 in the spark-ec2 repo. The only changes required on the spark_ec2.py script is to open the RM port.

cc andrewor14

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #6376 from shivaram/spark-ec2-yarn and squashes the following commits:

961504a [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into spark-ec2-yarn
152c94c [Shivaram Venkataraman] Open 8088 for YARN in EC2