[SPARK-4994][network]Cleanup removed executors' ShuffleInfo in yarn shuffle service

when the application is completed, yarn's nodemanager can remove application's local-dirs.but all executors' metadata of completed application havenot be removed. now it lets yarn ShuffleService to have much more memory to store Executors' ShuffleInfo. so these metadata need to be removed.

Author: lianhuiwang <lianhuiwang09@gmail.com>

Closes #3828 from lianhuiwang/SPARK-4994 and squashes the following commits:

f3ba1d2 [lianhuiwang] Cleanup removed executors' ShuffleInfo

network/yarn/src/main/java/org/apache/spark/network/yarn/YarnShuffleService.java

@@ -76,6 +76,9 @@ public class YarnShuffleService extends AuxiliaryService {
   // The actual server that serves shuffle files
   private TransportServer shuffleServer = null;
 
+  // Handles registering executors and opening shuffle blocks
+  private ExternalShuffleBlockHandler blockHandler;
+
   public YarnShuffleService() {
     super("spark_shuffle");
     logger.info("Initializing YARN shuffle service for Spark");
@@ -99,7 +102,8 @@ public class YarnShuffleService extends AuxiliaryService {
     // If authentication is enabled, set up the shuffle server to use a
     // special RPC handler that filters out unauthenticated fetch requests
     boolean authEnabled = conf.getBoolean(SPARK_AUTHENTICATE_KEY, DEFAULT_SPARK_AUTHENTICATE);
-    RpcHandler rpcHandler = new ExternalShuffleBlockHandler(transportConf);
+    blockHandler = new ExternalShuffleBlockHandler(transportConf);
+    RpcHandler rpcHandler = blockHandler;
     if (authEnabled) {
       secretManager = new ShuffleSecretManager();
       rpcHandler = new SaslRpcHandler(rpcHandler, secretManager);
@@ -136,6 +140,7 @@ public class YarnShuffleService extends AuxiliaryService {
       if (isAuthenticationEnabled()) {
         secretManager.unregisterApp(appId);
       }
+      blockHandler.applicationRemoved(appId, false /* clean up local dirs */);
     } catch (Exception e) {
       logger.error("Exception when stopping application {}", appId, e);
     }