Provide reasons for expect failures in service test helper.

tests/standalone/vmservice/multiple_isolate_list_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.
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 //
 // Test:
 //   *) Connect to VM Service and obtain list of running isolates.
-//   *) Spawn a second isolate and run test again.
 
 library multiple_isolate_list_test;
 
 import 'test_helper.dart';
 import 'package:expect/expect.dart';
 
 class MultipleIsolateListTest extends VmServiceRequestHelper {
   MultipleIsolateListTest(port) : super('http://127.0.0.1:$port/isolates');
 
   onRequestCompleted(Map reply) {
     IsolateListTester tester = new IsolateListTester(reply);
     tester.checkIsolateCount(2);
     tester.checkIsolateIdExists(7116);
     tester.checkIsolateNamePrefix(7116, 'multiple_isolate_list_script.dart');
     tester.checkIsolateNameContains('myIsolateName');
   }
 }
 
 main() {
   var process = new TestLauncher('multiple_isolate_list_script.dart');
   process.launch().then((port) {
     var test = new MultipleIsolateListTest(port);
     test.makeRequest().then((_) {
       process.requestExit();
     });
   });
 }