AMBARI-21695. Problem in starting accumulo in upgraded cluster (IOP-HDP). UT fix ammended. (swagle)

ambari-server/src/main/java/org/apache/ambari/server/events/listeners/upgrade/StackUpgradeFinishListener.java

@@ -90,7 +90,7 @@ public class StackUpgradeFinishListener {
       // Clear the RoleCommandOrder cache on upgrade
       if (roleCommandOrderProvider.get() instanceof CachedRoleCommandOrderProvider) {
         LOG.info("Clearing RCO cache");
-        CachedRoleCommandOrderProvider cachedRcoProvider = (CachedRoleCommandOrderProvider) roleCommandOrderProvider;
+        CachedRoleCommandOrderProvider cachedRcoProvider = (CachedRoleCommandOrderProvider) roleCommandOrderProvider.get();
         cachedRcoProvider.clearRoleCommandOrderCache();
       }
     }