[SPARK-2258 / 2266] Fix a few worker UI bugs

**SPARK-2258.** Worker UI displays zombie processes if the executor throws an exception before a process is launched. This is because we only inform the Worker of the change if the process is already launched, which in this case it isn't.

**SPARK-2266.** We expose "Some(app-id)" on the log page. This is fairly minor.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1213 from andrewor14/fix-worker-ui and squashes the following commits:

c1223fe [Andrew Or] Fix worker UI bugs

core/src/main/scala/org/apache/spark/deploy/worker/ExecutorRunner.scala

@@ -77,6 +77,7 @@ private[spark] class ExecutorRunner(
    * @param message the exception message which caused the executor's death 
    */
   private def killProcess(message: Option[String]) {
+    var exitCode: Option[Int] = None
     if (process != null) {
       logInfo("Killing process!")
       process.destroy()
@@ -87,9 +88,9 @@ private[spark] class ExecutorRunner(
       if (stderrAppender != null) {
         stderrAppender.stop()
       }
-      val exitCode = process.waitFor()
-      worker ! ExecutorStateChanged(appId, execId, state, message, Some(exitCode))
+      exitCode = Some(process.waitFor())
     }
+    worker ! ExecutorStateChanged(appId, execId, state, message, exitCode)
   }
 
   /** Stop this executor runner, including killing the process it launched */

core/src/main/scala/org/apache/spark/deploy/worker/ui/LogPage.scala

@@ -120,7 +120,7 @@ private[spark] class LogPage(parent: WorkerWebUI) extends WebUIPage("logPage") w
           </div>
         </body>
       </html>
-    UIUtils.basicSparkPage(content, logType + " log page for " + appId)
+    UIUtils.basicSparkPage(content, logType + " log page for " + appId.getOrElse("unknown app"))
   }
 
   /** Get the part of the log files given the offset and desired length of bytes */