(1 of 2) Refactor and move Autotest downloader to the Dev Server.

Added two new Dev Server handlers:
1. Given GS url, download and install the build image.
2. Return the control file for a particular build.

BUG=chromium-os:22954
TEST=manual

Change-Id: Id3914a5ee429bea8c9b64fe74a21958459669a20
Reviewed-on: https://gerrit.chromium.org/gerrit/12802
Commit-Ready: Frank Farzan <frankf@chromium.org>
Reviewed-by: Frank Farzan <frankf@chromium.org>
Tested-by: Frank Farzan <frankf@chromium.org>
diff --git a/constants.py b/constants.py
new file mode 100644
index 0000000..e5fcdd4
--- /dev/null
+++ b/constants.py
@@ -0,0 +1,10 @@
+# Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import os
+
+# Used for importing chromite which is expected to be 3 levels up from
+# this file.
+SOURCE_ROOT = os.path.join(os.path.dirname(__file__), os.pardir, os.pardir,
+                           os.pardir)