AMBARI-6012. ATS start fails on due to ClassNotFoundException. (mahadev)

ambari-server/src/main/resources/stacks/HDP/2.1/services/YARN/configuration/yarn-site.xml

@@ -349,7 +349,7 @@
 
   <property>
     <name>yarn.timeline-service.store-class</name>
-    <value>org.apache.hadoop.yarn.server.applicationhistoryservice.timeline.LeveldbTimelineStore</value>
+    <value>org.apache.hadoop.yarn.server.timeline.LeveldbTimelineStore</value>
     <description>
       Store class name for timeline store
     </description>