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/api.py b/api/controller/api.py
index d3b3220..e0c5d5a 100644
--- a/api/controller/api.py
+++ b/api/controller/api.py
@@ -7,6 +7,7 @@
 
 from __future__ import print_function
 
+from chromite.api import faux
 from chromite.api import router as router_lib
 from chromite.api import validate
 
@@ -19,6 +20,7 @@
 VERSION_BUG = 0
 
 
+@faux.all_empty
 @validate.validation_complete
 def GetMethods(_input_proto, output_proto, _config):
   """List all of the registered methods."""