Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/https_client_certificate_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import "dart:async";
+import "dart:io";
+
+import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 import "package:path/path.dart";
-import "dart:async";
-import "dart:io";
-import "dart:isolate";
 
 const HOST_NAME = "localhost";
 
 
 Function test() {
-  var keepAlive = new ReceivePort();
+  asyncStart();
   HttpServer.bindSecure(HOST_NAME,
                         0,
                         backlog: 5,
                         certificateName: 'localhost_cert',
                         requestClientCertificate: true).then((server) {
     server.listen((HttpRequest request) {
       Expect.isNotNull(request.certificate);
       Expect.equals('CN=localhost', request.certificate.subject);
       request.response.write("Hello");
       request.response.close();
     });
 
     HttpClient client = new HttpClient();
     client.getUrl(Uri.parse("https://$HOST_NAME:${server.port}/"))
         .then((request) => request.close())
         .then((response) {
           Expect.equals('CN=localhost', response.certificate.subject);
           Expect.equals('CN=myauthority', response.certificate.issuer);
           return response.fold(<int>[],
                                (message, data) => message..addAll(data));
         })
         .then((message) {
           String received = new String.fromCharCodes(message);
           Expect.equals(received, "Hello");
           client.close();
           server.close();
-          keepAlive.close();
+          asyncEnd();
         });
   });
 }
 
 void InitializeSSL() {
   var testPkcertDatabase = join(dirname(Platform.script), 'pkcert');
   SecureSocket.initialize(database: testPkcertDatabase,
                           password: 'dartdart');
 }
 
 void main() {
   InitializeSSL();
   test();
 }