MAPREDUCE-6521. MiniMRYarnCluster should not create /tmp/hadoop-yarn/staging on local filesystem in unit test.

Contributed by Masatake Iwasaki.

Change-Id: Id74b90eb7cfb9d676188fc5aa47249ee8904a3d5

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapreduce/v2/MiniMRYarnCluster.java

@@ -119,7 +119,9 @@ public class MiniMRYarnCluster extends MiniYARNCluster {
   @Override
   public void serviceInit(Configuration conf) throws Exception {
     conf.set(MRConfig.FRAMEWORK_NAME, MRConfig.YARN_FRAMEWORK_NAME);
-    if (conf.get(MRJobConfig.MR_AM_STAGING_DIR) == null) {
+    String stagingDir = conf.get(MRJobConfig.MR_AM_STAGING_DIR);
+    if (stagingDir == null ||
+        stagingDir.equals(MRJobConfig.DEFAULT_MR_AM_STAGING_DIR)) {
       conf.set(MRJobConfig.MR_AM_STAGING_DIR, new File(getTestWorkDir(),
           "apps_staging_dir/").getAbsolutePath());
     }