[SPARK-5641] [EC2] Allow spark_ec2.py to copy arbitrary files to cluster

Give users an easy way to rcp a directory structure to the master's / as part of the cluster launch, at a useful point in the workflow (before setup.sh is called on the master).

This is an alternative approach to meeting requirements discussed in https://github.com/apache/spark/pull/4487

Author: Florian Verhein <florian.verhein@gmail.com>

Closes #4583 from florianverhein/master and squashes the following commits:

49dee88 [Florian Verhein] removed addition of trailing / in rsync to give user this option, added documentation in help
7b8e3d8 [Florian Verhein] remove unused args
87d922c [Florian Verhein] [SPARK-5641] [EC2] implement --deploy-root-dir