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

test/get/git/doesnt_fetch_if_nothing_changes_test.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.
 
 import 'package:path/path.dart' as p;
 import 'package:pub/src/io.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   integration("doesn't re-fetch a repository if nothing changes", () {
     ensureGit();
 
     var repo = d.git('foo.git', [
       d.libDir('foo'),
       d.libPubspec('foo', '1.0.0')
     ]);
     repo.create();
 
     d.appDir({
       "foo": {"git": {"url": "../foo.git"}}
     }).create();
 
-    pubGet();
+    pubGet(args: ["--packages-dir"]);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo";')
       ])
     ]).validate();
 
     // Delete the repo. This will cause "pub get" to fail if it tries to
     // re-fetch.
     schedule(() => deleteEntry(p.join(sandboxDir, 'foo.git')));
 
-    pubGet();
+    pubGet(args: ["--packages-dir"]);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo";')
       ])
     ]).validate();
   });
 }