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_unittest.py b/api/controller/image_unittest.py
index d160287..46efa5e 100644
--- a/api/controller/image_unittest.py
+++ b/api/controller/image_unittest.py
@@ -10,9 +10,10 @@
 import mock
 import os
 
+from chromite.api import controller
+from chromite.api.controller import image as image_controller
 from chromite.api.gen.chromite.api import image_pb2
 from chromite.api.gen.chromiumos import common_pb2
-from chromite.api.controller import image as image_controller
 from chromite.lib import constants
 from chromite.lib import cros_build_lib
 from chromite.lib import cros_test_lib
@@ -100,7 +101,8 @@
     input_proto.build_target.name = 'board'
     output_proto = image_pb2.CreateImageResult()
 
-    image_controller.Create(input_proto, output_proto)
+    rc = image_controller.Create(input_proto, output_proto)
+    self.assertEqual(controller.RETURN_CODE_UNSUCCESSFUL_RESPONSE_AVAILABLE, rc)
     for package in output_proto.failed_packages:
       self.assertIn((package.category, package.package_name), expected_packages)