[SPARK-4989][CORE] avoid wrong eventlog conf cause cluster down in standalone mode

when enabling eventlog in standalone mode, if give the wrong configuration, the standalone cluster will down (cause master restart, lose connection with workers).
How to reproduce: just give an invalid value to "spark.eventLog.dir", for example: spark.eventLog.dir=hdfs://tmp/logdir1, hdfs://tmp/logdir2. This will throw illegalArgumentException, which will cause the Master restart. And the whole cluster is not available.

Author: Zhang, Liye <liye.zhang@intel.com>

Closes #3824 from liyezhang556520/wrongConf4Cluster and squashes the following commits:

3c24d98 [Zhang, Liye] revert change with logwarning and excetption for FileNotFoundException
3c1ac2e [Zhang, Liye] change var to val
a49c52f [Zhang, Liye] revert wrong modification
12eee85 [Zhang, Liye] add more message in log and on webUI
5c1fa33 [Zhang, Liye] cache exceptions when eventlog with wrong conf

core/src/main/scala/org/apache/spark/deploy/master/Master.scala

@@ -720,26 +720,27 @@ private[spark] class Master(
   def rebuildSparkUI(app: ApplicationInfo): Boolean = {
     val appName = app.desc.name
     val notFoundBasePath = HistoryServer.UI_PATH_PREFIX + "/not-found"
-    val eventLogFile = app.desc.eventLogDir
-      .map { dir => EventLoggingListener.getLogPath(dir, app.id) }
-      .getOrElse {
-        // Event logging is not enabled for this application
-        app.desc.appUiUrl = notFoundBasePath
-        return false
-    }
-    val fs = Utils.getHadoopFileSystem(eventLogFile, hadoopConf)
+    try {
+      val eventLogFile = app.desc.eventLogDir
+        .map { dir => EventLoggingListener.getLogPath(dir, app.id) }
+        .getOrElse {
+          // Event logging is not enabled for this application
+          app.desc.appUiUrl = notFoundBasePath
+          return false
+        }
+        
+      val fs = Utils.getHadoopFileSystem(eventLogFile, hadoopConf)
 
-    if (fs.exists(new Path(eventLogFile + EventLoggingListener.IN_PROGRESS))) {
-      // Event logging is enabled for this application, but the application is still in progress
-      val title = s"Application history not found (${app.id})"
-      var msg = s"Application $appName is still in progress."
-      logWarning(msg)
-      msg = URLEncoder.encode(msg, "UTF-8")
-      app.desc.appUiUrl = notFoundBasePath + s"?msg=$msg&title=$title"
-      return false
-    }
+      if (fs.exists(new Path(eventLogFile + EventLoggingListener.IN_PROGRESS))) {
+        // Event logging is enabled for this application, but the application is still in progress
+        val title = s"Application history not found (${app.id})"
+        var msg = s"Application $appName is still in progress."
+        logWarning(msg)
+        msg = URLEncoder.encode(msg, "UTF-8")
+        app.desc.appUiUrl = notFoundBasePath + s"?msg=$msg&title=$title"
+        return false
+      }
 
-    try {
       val (logInput, sparkVersion) = EventLoggingListener.openEventLog(new Path(eventLogFile), fs)
       val replayBus = new ReplayListenerBus()
       val ui = SparkUI.createHistoryUI(new SparkConf, replayBus, new SecurityManager(conf),
@@ -758,7 +759,7 @@ private[spark] class Master(
       case fnf: FileNotFoundException =>
         // Event logging is enabled for this application, but no event logs are found
         val title = s"Application history not found (${app.id})"
-        var msg = s"No event logs found for application $appName in $eventLogFile."
+        var msg = s"No event logs found for application $appName in ${app.desc.eventLogDir}."
         logWarning(msg)
         msg += " Did you specify the correct logging directory?"
         msg = URLEncoder.encode(msg, "UTF-8")