[SPARK-1953][YARN]yarn client mode Application Master memory size is same as driver memory...

... size

Ways to set Application Master's memory on yarn-client mode:
1.  `spark.yarn.am.memory` in SparkConf or System Properties
2.  default value 512m

Note: this arguments is only available in yarn-client mode.


I find it more confusing. It's immediately intuitive that `spark.yarn.am.memoryOverhead` is the overhead applied on top of `spark.yarn.am.memory` since they share the same prefix, but it's not at all clear to me that `spark.driver.memoryOverhead` is related at all (assuming the user does not have expertise in how different deploy modes are architected).