Ensure server.stop() is called when shutting down.

Also remove the cleanup code from the fs provider. It would be
better to clean up, but there's a race between that code's cleanup
and Hadoop's shutdown hook, which closes all file systems kept in
the cache. So if you try to clean up the fs provider in a shut
down hook, you may end up with ugly exceptions in the output.

But leave the stop() functionality around in case it's useful for
future provider implementations.

core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala

@@ -54,7 +54,7 @@ class FsHistoryProvider(conf: SparkConf) extends ApplicationHistoryProvider
    */
   private val logCheckingThread = new Thread("LogCheckingThread") {
     override def run() = Utils.logUncaughtExceptions {
-      while (!stopped) {
+      while (true) {
         val now = System.currentTimeMillis
         if (now - lastLogCheckTime > UPDATE_INTERVAL_MS) {
           Thread.sleep(UPDATE_INTERVAL_MS)
@@ -68,8 +68,6 @@ class FsHistoryProvider(conf: SparkConf) extends ApplicationHistoryProvider
     }
   }
 
-  @volatile private var stopped = false
-
   initialize()
 
   private def initialize() {
@@ -87,13 +85,6 @@ class FsHistoryProvider(conf: SparkConf) extends ApplicationHistoryProvider
     logCheckingThread.start()
   }
 
-  override def stop() = {
-    stopped = true
-    logCheckingThread.interrupt()
-    logCheckingThread.join()
-    fs.close()
-  }
-
   override def getListing(offset: Int, count: Int) = {
     val list = appList.get()
     val theOffset = if (offset < list.size) offset else 0

core/src/main/scala/org/apache/spark/deploy/history/HistoryServer.scala

@@ -195,9 +195,14 @@ object HistoryServer {
     val server = new HistoryServer(conf, provider, securityManager, port)
     server.bind()
 
+    Runtime.getRuntime().addShutdownHook(new Thread("HistoryServerStopper") {
+        override def run() = {
+          server.stop()
+        }
+      })
+
     // Wait until the end of the world... or if the HistoryServer process is manually stopped
     while(true) { Thread.sleep(Int.MaxValue) }
-    server.stop()
   }
 
   def initSecurity() {