[SPARK-7451] [YARN] Preemption of executors is counted as failure causing Spark job to fail

Added a check to handle container exit status for the preemption scenario, log an INFO message in such cases and move on.
andrewor14

Author: Ashwin Shankar <ashankar@netflix.com>

Closes #5993 from ashwinshankar77/SPARK-7451 and squashes the following commits:

90900cf [Ashwin Shankar] Fix log info message
cf8b6cf [Ashwin Shankar] Stop counting preemption of executors as failure

yarn/src/main/scala/org/apache/spark/deploy/yarn/YarnAllocator.scala

@@ -373,7 +373,9 @@ private[yarn] class YarnAllocator(
         // Hadoop 2.2.X added a ContainerExitStatus we should switch to use
         // there are some exit status' we shouldn't necessarily count against us, but for
         // now I think its ok as none of the containers are expected to exit
-        if (completedContainer.getExitStatus == -103) { // vmem limit exceeded
+        if (completedContainer.getExitStatus == ContainerExitStatus.PREEMPTED) {
+          logInfo("Container preempted: " + containerId)
+        } else if (completedContainer.getExitStatus == -103) { // vmem limit exceeded
           logWarning(memLimitExceededLogMessage(
             completedContainer.getDiagnostics,
             VMEM_EXCEEDED_PATTERN))