Update unittest to new package layout.

pkg/unittest/lib/vm_config.dart

 // Copyright (c) 2012, 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.
 
 /**
  * A simple unit test library for running tests on the VM.
  */
 #library('unittest');
 
 #import('dart:io');
 #import('unittest.dart');
 
 class VmConfiguration extends Configuration {
   void onDone(int passed, int failed, int errors, List<TestCase> results,
       String uncaughtError) {
     try {
       super.onDone(passed, failed, errors, results, uncaughtError);
     } on Exception catch (ex) {
       // A non-zero exit code is used by the test infrastructure to detect
       // failure.
       exit(1);
     }
   }
 }
 
 void useVmConfiguration() {
   configure(new VmConfiguration());
 }