devserver: Add quick_provision stage artifact.

BUG=chromium:779870
TEST=curl "http://${ds}/stage?archive_url=gs://chromeos-image-archive/${build}&artifacts=quick_provision"

Change-Id: I1b8949fdff93cba06d19a5264e1485741dd253bc
Reviewed-on: https://chromium-review.googlesource.com/751791
Commit-Ready: David Riley <davidriley@chromium.org>
Tested-by: David Riley <davidriley@chromium.org>
Reviewed-by: Xixuan Wu <xixuan@chromium.org>
diff --git a/artifact_info.py b/artifact_info.py
index bf3c74e..19081ed 100644
--- a/artifact_info.py
+++ b/artifact_info.py
@@ -35,6 +35,9 @@
 # The developer image - the base image with developer enhancements.
 DEV_IMAGE = 'dev_image'
 
+# The name of artifact to stage a quick provision payload.
+QUICK_PROVISION = 'quick_provision'
+
 #### Autotest related packages. ####
 
 # Autotest -- the main autotest directory without the test_suites subdir.