Make "--no-packages-dir" the default.

test/get/git/check_out_branch_test.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.
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   integration('checks out a package at a specific branch from Git', () {
     ensureGit();
 
     var repo = d.git('foo.git', [
       d.libDir('foo', 'foo 1'),
       d.libPubspec('foo', '1.0.0')
     ]);
     repo.create();
     repo.runGit(["branch", "old"]);
 
     d.git('foo.git', [
       d.libDir('foo', 'foo 2'),
       d.libPubspec('foo', '1.0.0')
     ]).commit();
 
     d.appDir({
       "foo": {"git": {"url": "../foo.git", "ref": "old"}}
     }).create();
 
-    pubGet();
+    pubGet(args: ["--packages-dir"]);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo 1";')
       ])
     ]).validate();
   });
 }