Build API: Standardize return codes.

BUG=chromium:963605
TEST=run_tests

Change-Id: If05654fe56e24425da1b89b8d516cc7ba6bebd3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1615507
Tested-by: Alex Klein <saklein@chromium.org>
Tested-by: David Burger <dburger@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
Reviewed-by: Evan Hernandez <evanhernandez@chromium.org>
diff --git a/api/controller/image.py b/api/controller/image.py
index da17256..84ae8f8 100644
--- a/api/controller/image.py
+++ b/api/controller/image.py
@@ -12,6 +12,7 @@
 
 import os
 
+from chromite.api import controller
 from chromite.api.gen.chromiumos import common_pb2
 from chromite.api.controller import controller_util
 from chromite.lib import cros_build_lib
@@ -76,7 +77,7 @@
       if package.version:
         current.version = package.version
 
-    return 1
+    return controller.RETURN_CODE_UNSUCCESSFUL_RESPONSE_AVAILABLE
 
   if not vm_types:
     # No VMs to build, we can exit now.
@@ -209,5 +210,10 @@
     cros_build_lib.Die(
         'The image.path must be an existing image file with a .bin extension.')
 
-  output_proto.success = image.Test(board, result_directory,
-                                    image_dir=image_path)
+  success = image.Test(board, result_directory, image_dir=image_path)
+  output_proto.success = success
+
+  if success:
+    return controller.RETURN_CODE_SUCCESS
+  else:
+    return controller.RETURN_CODE_COMPLETED_UNSUCCESSFULLY