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/image.py b/api/controller/image.py
index ca3aa15..937d582 100644
--- a/api/controller/image.py
+++ b/api/controller/image.py
@@ -65,7 +65,7 @@
 
 
 @faux.success(_CreateResponse)
-@faux.empty_error
+@faux.empty_completed_unsuccessfully_error
 @validate.require('build_target.name')
 @validate.validation_complete
 @metrics.collect_metrics
@@ -201,7 +201,7 @@
 
 
 @faux.success(_SignerTestResponse)
-@faux.empty_error
+@faux.empty_completed_unsuccessfully_error
 @validate.exists('image.path')
 @validate.validation_complete
 def SignerTest(input_proto, output_proto, _config):
@@ -229,7 +229,7 @@
 
 
 @faux.success(_TestResponse)
-@faux.empty_error
+@faux.empty_completed_unsuccessfully_error
 @validate.require('build_target.name', 'result.directory')
 @validate.exists('image.path')
 def Test(input_proto, output_proto, config):