[SPARK-19792][WEBUI] In the Master Page,the column named “Memory per …

…Node” ,I think it is not all right

Signed-off-by: liuxian <liu.xian3zte.com.cn>

## What changes were proposed in this pull request?

Open the spark web page,in the Master Page ,have two tables:Running Applications table and Completed Applications table, to the column named “Memory per Node” ,I think it is not all right ,because a node may be not have only one executor.So I think that should be named as “Memory per Executor”.Otherwise easy to let the user misunderstanding

## How was this patch tested?

N/A

Author: liuxian <liu.xian3@zte.com.cn>

Closes #17132 from 10110346/wid-lx-0302.

core/src/main/scala/org/apache/spark/deploy/master/ui/MasterPage.scala

@@ -76,7 +76,7 @@ private[ui] class MasterPage(parent: MasterWebUI) extends WebUIPage("") {
     val aliveWorkers = state.workers.filter(_.state == WorkerState.ALIVE)
     val workerTable = UIUtils.listingTable(workerHeaders, workerRow, workers)
 
-    val appHeaders = Seq("Application ID", "Name", "Cores", "Memory per Node", "Submitted Time",
+    val appHeaders = Seq("Application ID", "Name", "Cores", "Memory per Executor", "Submitted Time",
       "User", "State", "Duration")
     val activeApps = state.activeApps.sortBy(_.startTime).reverse
     val activeAppsTable = UIUtils.listingTable(appHeaders, appRow, activeApps)