SPARK-1652: Spark submit should fail gracefully if YARN not enabled

Author: Patrick Wendell <pwendell@gmail.com>

Closes #579 from pwendell/spark-submit-yarn-2 and squashes the following commits:

05e1b11 [Patrick Wendell] Small fix
d2a40ad [Patrick Wendell] SPARK-1652: Spark submit should fail gracefully if YARN support not enabled
SPARK-1654 and SPARK-1653: Fixes in spark-submit.

Deals with two issues:
1. Spark shell didn't correctly pass quoted arguments to spark-submit.
```./bin/spark-shell --driver-java-options "-Dfoo=f -Dbar=b"```
2. Spark submit used deprecated environment variables (SPARK_CLASSPATH)
   which triggered warnings. Now we use new, more narrowly scoped,
   variables.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #576 from pwendell/spark-submit and squashes the following commits:

67004c9 [Patrick Wendell] SPARK-1654 and SPARK-1653: Fixes in spark-submit.