Teach the devserver to stage factory images.

Changes to the devserver that allow us to stage images
from the factory branch.

TEST=Staged factory images and reimaged a device.
BUG=chromium:252503

Change-Id: I51f710996e63b4a8d3a772688cdc5643a423b511
Reviewed-on: https://gerrit.chromium.org/gerrit/64034
Commit-Queue: Prashanth Balasubramanian <beeps@chromium.org>
Reviewed-by: Prashanth Balasubramanian <beeps@chromium.org>
Tested-by: Prashanth Balasubramanian <beeps@chromium.org>
diff --git a/gsutil_util.py b/gsutil_util.py
index 25b7da8..8373047 100644
--- a/gsutil_util.py
+++ b/gsutil_util.py
@@ -130,7 +130,10 @@
       msg = 'Failed to list payloads.'
       returned_list = GSUtilRun(cmd, msg).splitlines()
       for item in returned_list:
-        uploaded_list.append(item.rsplit('/', 1)[1])
+        try:
+          uploaded_list.append(item.rsplit('/', 1)[1])
+        except IndexError:
+          pass
 
     # Check if all target artifacts are available.
     found_names = _GetGSNamesFromList(uploaded_list, pattern)