Process outstanding events before making a new HTTP client request

tests/standalone/io/https_bad_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.
 
 // This test verifies that the bad certificate callback works in HttpClient.
 
 import "package:expect/expect.dart";
 import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 
 const HOST_NAME = "localhost";
 const CERTIFICATE = "localhost_cert";
 
 Future<SecureServerSocket> runServer() {
   SecureSocket.initialize(
       database: Platform.script.resolve('pkcert').toFilePath(),
       password: 'dartdart');
 
   return HttpServer.bindSecure(
       HOST_NAME, 0, backlog: 5, certificateName: 'localhost_cert')
   .then((server) {
     server.listen((HttpRequest request) {
       request.listen((_) { }, onDone: () { request.response.close(); });
     }, onError: (e) { if (e is! HandshakeException) throw e; });
     return server;
   });
 }
 
-void main() {
+main() async {
   var clientScript = Platform.script
                              .resolve('https_bad_certificate_client.dart')
                              .toFilePath();
   Future clientProcess(int port, String acceptCertificate) {
     return Process.run(Platform.executable,
         [clientScript, port.toString(), acceptCertificate])
     .then((ProcessResult result) {
       if (result.exitCode != 0 || !result.stdout.contains('SUCCESS')) {
         print("Client failed, acceptCertificate: $acceptCertificate");
         print("  stdout:");
         print(result.stdout);
         print("  stderr:");
         print(result.stderr);
         Expect.fail('Client subprocess exit code: ${result.exitCode}');
       }
     });
   }
 
-  runServer().then((server) {
-    Future.wait([clientProcess(server.port, 'true'),
-                 clientProcess(server.port, 'false'),
-                 clientProcess(server.port, 'fisk'),
-                 clientProcess(server.port, 'exception')]).then((_) {
-      server.close();
-    });
-  });
+  var server = await runServer();
+  await clientProcess(server.port, 'true');
+  await clientProcess(server.port, 'false');
+  await clientProcess(server.port, 'fisk');
+  await clientProcess(server.port, 'exception');
+  server.close();
 }