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/android.py b/api/controller/android.py
index 29e408b..1500ef8 100644
--- a/api/controller/android.py
+++ b/api/controller/android.py
@@ -9,6 +9,7 @@
 
 import os
 
+from chromite.api import faux
 from chromite.api import validate
 from chromite.api.controller import controller_util
 from chromite.api.gen.chromite.api import android_pb2
@@ -24,6 +25,7 @@
                                     'package.mask', 'androidpin')
 
 
+@faux.all_empty
 @validate.require('tracking_branch', 'package_name', 'android_build_branch')
 @validate.validation_complete
 def MarkStable(input_proto, output_proto, _config):
@@ -74,6 +76,7 @@
     output_proto.status = android_pb2.MARK_STABLE_STATUS_EARLY_EXIT
 
 
+@faux.all_empty
 @validate.validation_complete
 def UnpinVersion(_input_proto, _output_proto, _config):
   """Unpin the Android version.