Build API: Adding mock responses.

Complete mock responses for the api, sdk, and sysroot controllers.
Added empty mock responses for the rest of the endpoints, and bugs
have been created to complete them.

BUG=chromium:999178
TEST=run_tests

Change-Id: Ib9ead797a588a9f4ccf50a6a663ab7dbdf5d0ae8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1787937
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Tested-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
diff --git a/api/controller/image.py b/api/controller/image.py
index 88d2d52..b7d51eb 100644
--- a/api/controller/image.py
+++ b/api/controller/image.py
@@ -13,6 +13,7 @@
 import os
 
 from chromite.api import controller
+from chromite.api import faux
 from chromite.api import validate
 from chromite.api.gen.chromiumos import common_pb2
 from chromite.lib import cros_build_lib
@@ -52,6 +53,7 @@
 }
 
 
+@faux.all_empty
 @validate.require('build_target.name')
 @validate.validation_complete
 def Create(input_proto, output_proto, _config):
@@ -172,6 +174,7 @@
     new_image.build_target.name = board
 
 
+@faux.all_empty
 @validate.exists('image.path')
 @validate.validation_complete
 def SignerTest(input_proto, output_proto, _config):
@@ -191,6 +194,8 @@
   else:
     return controller.RETURN_CODE_COMPLETED_UNSUCCESSFULLY
 
+
+@faux.all_empty
 @validate.require('build_target.name', 'result.directory')
 @validate.exists('image.path')
 def Test(input_proto, output_proto, config):