SPARK-1689: Spark application should die when removed by Master

scheduler.error() will mask the error if there are active tasks. Being removed is a cataclysmic event for Spark applications, and should probably be treated as such.

Author: Aaron Davidson <aaron@databricks.com>

Closes #832 from aarondav/i-love-u and squashes the following commits:

9f1200f [Aaron Davidson] SPARK-1689: Spark application should die when removed by Master