xbuddy: Fix delta_payload artifact

delta_payload artifact currently not working. This CL fixes it. Also:

This API now puts the artifacts in 'au_nton' subdirectory of the build
in static_dir of the devserver.

Remove M to N payloads. We don't have these concepts at this level
anymore.

BUG=chromium:793434
TEST=changed cros flash to get delta_payloads and it succeeded.
TEST=build_artifact_unittest
TEST=CQ passes

Change-Id: I7034ca63b6ee6313762d01f31cee816b5d88e5c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2055790
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: David Haddock <dhaddock@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
diff --git a/cli/flash.py b/cli/flash.py
index 7e7879a..902b193 100644
--- a/cli/flash.py
+++ b/cli/flash.py
@@ -29,6 +29,8 @@
 from chromite.lib.paygen import paygen_payload_lib
 from chromite.lib.paygen import paygen_stateful_payload_lib
 
+from chromite.lib.xbuddy import artifact_info
+
 
 DEVSERVER_STATIC_DIR = path_util.FromChrootPath(
     os.path.join(constants.CHROOT_SOURCE_ROOT, 'devserver', 'static'))
@@ -443,14 +445,14 @@
       # fails, fallback to downloading the image.
       try:
         translated_path, _ = ds_wrapper.GetImagePathWithXbuddy(
-            os.path.join(self.image, 'full_payload'), self.board,
+            os.path.join(self.image, artifact_info.FULL_PAYLOAD), self.board,
             static_dir=DEVSERVER_STATIC_DIR, silent=True)
         payload_dir = os.path.dirname(
             ds_wrapper.TranslatedPathToLocalPath(translated_path,
                                                  DEVSERVER_STATIC_DIR))
         ds_wrapper.GetImagePathWithXbuddy(
-            os.path.join(self.image, 'stateful'), self.board,
-            static_dir=DEVSERVER_STATIC_DIR, silent=True)
+            os.path.join(self.image, artifact_info.STATEFUL_PAYLOAD),
+            self.board, static_dir=DEVSERVER_STATIC_DIR, silent=True)
         fetch_image = False
       except (ds_wrapper.ImagePathError, ds_wrapper.ArtifactDownloadError):
         logging.info('Could not find full_payload or stateful for "%s"',