veyron.core: Fix tests that leave files in /tmp

This change fixes the tests that leave files in /tmp after returning
successfully. The goal is to leave no temporary files.

Change-Id: I1d5df68995472bbda98fb2aee1ac64cd57d4de4e
diff --git a/tools/binary/impl_test.go b/tools/binary/impl_test.go
index 865c35d..180b53c 100644
--- a/tools/binary/impl_test.go
+++ b/tools/binary/impl_test.go
@@ -138,7 +138,7 @@
 	if err != nil {
 		t.Fatalf("%v", err)
 	}
-	defer os.Remove(dir)
+	defer os.RemoveAll(dir)
 	file := path.Join(dir, "testfile")
 	defer os.Remove(file)
 	if err := cmd.Execute([]string{"download", naming.JoinAddressName(endpoint.String(), "exists"), file}); err != nil {