YARN-2566. DefaultContainerExecutor should pick a working directory randomly. (Zhihai Xu via kasha)

(cherry picked from commit cc93e7e683fa74eb1a7aa2b357a36667bd21086a)

Conflicts:
	hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/DefaultContainerExecutor.java