Refactor download API in the dev server.

Add comments and take named params.

BUG=chromium-os:24604
TEST=Ran dev server, verify download API works.

Change-Id: Ie7462e134dffe87f6e171e867ae62a752589a449
Reviewed-on: https://gerrit.chromium.org/gerrit/13593
Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Ready: Frank Farzan <frankf@chromium.org>
Tested-by: Frank Farzan <frankf@chromium.org>
diff --git a/devserver_util.py b/devserver_util.py
index 6ee02aa..9cdb3bb 100644
--- a/devserver_util.py
+++ b/devserver_util.py
@@ -74,14 +74,12 @@
   Args:
     staging_dir: Temp directory containing payloads and autotest packages.
     archive_url: Google Storage path to the build directory.
-        e.g. chromeos-image-archive/x86-generic-release/R17-1208.0.0-a1-b338.
+        e.g. gs://chromeos-image-archive/x86-generic/R17-1208.0.0-a1-b338.
     build: Full build string to look for; e.g. R17-1208.0.0-a1-b338.
 
   Raises:
     DevServerUtilError: If any steps in the process fail to complete.
   """
-  archive_url = 'gs://' + archive_url
-
   # Get a list of payloads from Google Storage.
   cmd = 'gsutil ls %s/*.bin' % archive_url
   msg = 'Failed to get a list of payloads.'