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

test/upgrade/git/upgrade_one_locked_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("upgrades one locked Git package but no others", () {
     ensureGit();
 
     d.git('foo.git', [
       d.libDir('foo'),
       d.libPubspec('foo', '1.0.0')
     ]).create();
 
     d.git('bar.git', [
       d.libDir('bar'),
       d.libPubspec('bar', '1.0.0')
     ]).create();
 
     d.appDir({
       "foo": {"git": "../foo.git"},
       "bar": {"git": "../bar.git"}
     }).create();
 
-    pubGet();
+    pubGet(args: ['--packages-dir']);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo";')
       ]),
       d.dir('bar', [
         d.file('bar.dart', 'main() => "bar";')
       ])
     ]).validate();
 
     d.git('foo.git', [
       d.libDir('foo', 'foo 2'),
       d.libPubspec('foo', '1.0.0')
     ]).commit();
 
     d.git('bar.git', [
       d.libDir('bar', 'bar 2'),
       d.libPubspec('bar', '1.0.0')
     ]).commit();
 
-    pubUpgrade(args: ['foo']);
+    pubUpgrade(args: ['--packages-dir', 'foo']);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo 2";')
       ]),
       d.dir('bar', [
         d.file('bar.dart', 'main() => "bar";')
       ])
     ]).validate();
   });
 }