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

test/test_pub.dart

Index: test/test_pub.dart
diff --git a/test/test_pub.dart b/test/test_pub.dart
index 4269750c70d3a34ebb059f4021e2977ab3d4205a..12848dc6475843cfd93a77ee920fb8c93c0dffc7 100644
--- a/test/test_pub.dart
+++ b/test/test_pub.dart
@@ -75,6 +75,10 @@ final String appPath = "myapp";
 /// to the sandbox directory.
 final String packagesPath = "$appPath/packages";
 
+/// The path of the ".packages" file in the mock app used for tests, relative
+/// to the sandbox directory.
+final String packagesFilePath = "$appPath/.packages";
+
 /// Set to true when the current batch of scheduled events should be aborted.
 bool _abortScheduled = false;