Roll Observatory packages and add a roll script

packages/cli_util/lib/cli_util.dart

 // Copyright (c) 2015, 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 cli_util;
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:which/which.dart';
@@ skipping 48 matching lines @@
 
   return null;
 }
 
 bool _isSdkDir(Directory dir) => _joinFile(dir, ['version']).existsSync();
 
 File _joinFile(Directory dir, List<String> files) {
   String pathFragment = files.join(Platform.pathSeparator);
   return new File("${dir.path}${Platform.pathSeparator}${pathFragment}");
 }