[SPARK-18027][YARN] .sparkStaging not clean on RM ApplicationNotFoundException

## What changes were proposed in this pull request?

Cleanup YARN staging dir on all `KILLED`/`FAILED` paths in `monitorApplication`

## How was this patch tested?

Existing tests

Author: Sean Owen <sowen@cloudera.com>

Closes #15598 from srowen/SPARK-18027.

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

@@ -1059,9 +1059,11 @@ private[spark] class Client(
         } catch {
           case e: ApplicationNotFoundException =>
             logError(s"Application $appId not found.")
+            cleanupStagingDir(appId)
             return (YarnApplicationState.KILLED, FinalApplicationStatus.KILLED)
           case NonFatal(e) =>
             logError(s"Failed to contact YARN for application $appId.", e)
+            // Don't necessarily clean up staging dir because status is unknown
             return (YarnApplicationState.FAILED, FinalApplicationStatus.FAILED)
         }
       val state = report.getYarnApplicationState