Switch analysis_server to use 'package:test'.

pkg/analysis_server/test/src/test_all.dart

 // Copyright (c) 2014, 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.
 
 library test.src;
 
-import 'package:unittest/unittest.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../utils.dart';
 import 'utilities/test_all.dart' as utilities_all;
 
 /**
  * Utility for manually running all tests.
  */
 main() {
   initializeTestEnvironment();
-  group('analysis_server', () {
+  defineReflectiveSuite(() {
     utilities_all.main();
-  });
+  }, name: 'analysis_server');
 }