BuildAPI: Use faux.empty_completed_unsuccessfully_error for tests.

BUG=chromium:1029872
TEST=run_tests

Change-Id: Id4be0f617e1a9ed1df545c2c7c2970dfbfd796cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1964694
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Michael Mortensen <mmortensen@google.com>
Tested-by: Michael Mortensen <mmortensen@google.com>
diff --git a/api/controller/payload.py b/api/controller/payload.py
index 6497883..7b85f17 100644
--- a/api/controller/payload.py
+++ b/api/controller/payload.py
@@ -23,7 +23,8 @@
 # We have more fields we might validate however, they're either
 # 'oneof' or allowed to be the empty value by design. If @validate
 # gets more complex in the future we can add more here.
-@faux.all_empty
+@faux.empty_success
+@faux.empty_completed_unsuccessfully_error
 @validate.require('bucket')
 def GeneratePayload(input_proto, output_proto, config):
   """Generate a update payload ('do paygen').