fix spark on yarn after the sparkConf changes

This fixes it so that spark on yarn now compiles and works after the sparkConf changes. 

There are also other issues I discovered along the way that are broken:
- mvn builds for yarn don't assemble correctly
- unset SPARK_EXAMPLES_JAR isn't handled properly anymore
- I'm pretty sure spark.conf doesn't actually work as its not distributed with yarn

those things can be fixed in separate pr unless others disagree.