SPARK-1252. On YARN, use container-log4j.properties for executors

container-log4j.properties is a file that YARN provides so that containers can have log4j.properties distinct from that of the NodeManagers.

Logs now go to syslog, and stderr and stdout just have the process's standard err and standard out.

I tested this on pseudo-distributed clusters for both yarn (Hadoop 2.2) and yarn-alpha (Hadoop 0.23.7)/