Update docs and remove old reference to --user option

docs/running-on-yarn.md

@@ -57,7 +57,6 @@ The command to launch the YARN Client is as follows:
       --master-memory <MEMORY_FOR_MASTER> \
       --worker-memory <MEMORY_PER_WORKER> \
       --worker-cores <CORES_PER_WORKER> \
-      --user <hadoop_user> \
       --queue <queue_name>
 
 For example:
@@ -77,5 +76,4 @@ The above starts a YARN Client programs which periodically polls the Application
 
 - When your application instantiates a Spark context it must use a special "yarn-standalone" master url. This starts the scheduler without forcing it to connect to a cluster. A good way to handle this is to pass "yarn-standalone" as an argument to your program, as shown in the example above.
 - We do not requesting container resources based on the number of cores. Thus the numbers of cores given via command line arguments cannot be guaranteed.
-- Currently, we have not yet integrated with hadoop security. If --user is present, the hadoop_user specified will be used to run the tasks on the cluster. If unspecified, current user will be used (which should be valid in cluster).
-  Once hadoop security support is added, and if hadoop cluster is enabled with security, additional restrictions would apply via delegation tokens passed.
+- The local directories used for spark will be the local directories configured for YARN (Hadoop Yarn config yarn.nodemanager.local-dirs). If the user specifies spark.local.dir, it will be ignored.