Switch analysis_server to use 'package:test'.

pkg/analysis_server/test/channel/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.channel.all;
 
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 import '../utils.dart';
 import 'byte_stream_channel_test.dart' as byte_stream_channel_test;
 import 'web_socket_channel_test.dart' as web_socket_channel_test;
 
 /**
  * Utility for manually running all tests.
  */
 main() {
   initializeTestEnvironment();
   group('computer', () {
     byte_stream_channel_test.main();
     web_socket_channel_test.main();
   });
 }