SPARK-1691: Support quoted arguments inside of spark-submit.

This is a fairly straightforward fix. The bug was reported by @vanzin and the fix was proposed by @deanwampler and myself. Please take a look!

Author: Patrick Wendell <pwendell@gmail.com>

Closes #609 from pwendell/quotes and squashes the following commits:

8bed767 [Patrick Wendell] SPARK-1691: Support quoted arguments inside of spark-submit.