[autotest] Teach the devserver to stage factory images.

To stage a factory image the client request needs to
be made with the url to the canary-channel.

CQ-DEPEND=CL:I51f710996e63b4a8d3a772688cdc5643a423b511
TEST=Staged images from the factory branch.
BUG=chromium:252503

Change-Id: I34e5a6db44ee3de0705115ea8c665aae7fb5b416
Reviewed-on: https://chromium-review.googlesource.com/64155
Reviewed-by: Dan Shi <dshi@chromium.org>
Tested-by: Prashanth Balasubramanian <beeps@chromium.org>
Commit-Queue: Prashanth Balasubramanian <beeps@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index 85f7b39..4ff51fc 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -150,12 +150,14 @@
 image_storage_server: gs://chromeos-image-archive/
 # chromeos-devserver{1,2,3,4,5}.cros
 dev_server: http://172.22.50.205:8082,http://172.22.50.2:8082,http://172.17.40.27:8082,http://172.17.40.28:8082,http://172.17.40.17:8082
+canary_channel_server: gs://chromeos-releases/canary-channel/
 # chromeos-crash1.cros
 crash_server: http://172.17.40.24:8082
 sharding_factor: 1
 infrastructure_user: chromeos-test
 
 firmware_url_pattern: %s/static/%s/firmware_from_source.tar.bz2
+factory_image_url_pattern: %s/static/canary-channel/%s/factory_test/chromiumos_factory_image.bin
 image_url_pattern: %s/update/%s
 log_url_pattern: http://%s/tko/retrieve_logs.cgi?job=/results/%s/
 package_url_pattern: %s/static/%s/autotest/packages