[Typo] Stoped -> Stopped

Author: Andrew Or <andrewor14@gmail.com>

Closes #847 from andrewor14/yarn-typo and squashes the following commits:

c1906af [Andrew Or] Stoped -> Stopped

yarn/common/src/main/scala/org/apache/spark/scheduler/cluster/YarnClientSchedulerBackend.scala

@@ -113,7 +113,7 @@ private[spark] class YarnClientSchedulerBackend(
   override def stop() {
     super.stop()
     client.stop()
-    logInfo("Stoped")
+    logInfo("Stopped")
   }
 
 }