[SPARK-4915][YARN] Fix classname to be specified for external shuffle service.

Author: Tsuyoshi Ozawa <ozawa.tsuyoshi@lab.ntt.co.jp>

Closes #3757 from oza/SPARK-4915 and squashes the following commits:

3b0d6d6 [Tsuyoshi Ozawa] Fix classname to be specified for external shuffle service.

docs/job-scheduling.md

@@ -98,7 +98,7 @@ pre-packaged distribution.
 2. Add this jar to the classpath of all `NodeManager`s in your cluster.
 3. In the `yarn-site.xml` on each node, add `spark_shuffle` to `yarn.nodemanager.aux-services`,
 then set `yarn.nodemanager.aux-services.spark_shuffle.class` to
-`org.apache.spark.yarn.network.YarnShuffleService`. Additionally, set all relevant
+`org.apache.spark.network.yarn.YarnShuffleService`. Additionally, set all relevant
 `spark.shuffle.service.*` [configurations](configuration.html).
 4. Restart all `NodeManager`s in your cluster.