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/binhost.py b/api/controller/binhost.py
index e92c8fd..8752297 100644
--- a/api/controller/binhost.py
+++ b/api/controller/binhost.py
@@ -13,6 +13,7 @@
 from six.moves import urllib
 
 from chromite.api import controller
+from chromite.api import faux
 from chromite.api import validate
 from chromite.api.controller import controller_util
 from chromite.api.gen.chromite.api import binhost_pb2
@@ -31,6 +32,7 @@
 }
 
 
+@faux.all_empty
 @validate.require('build_target.name')
 @validate.validation_complete
 def GetBinhosts(input_proto, output_proto, _config):
@@ -45,6 +47,7 @@
     new_binhost.package_index = 'Packages'
 
 
+@faux.all_empty
 @validate.require('build_target.name')
 @validate.validation_complete
 def GetPrivatePrebuiltAclArgs(input_proto, output_proto, _config):
@@ -62,6 +65,7 @@
     new_arg.value = value
 
 
+@faux.all_empty
 @validate.require('uri')
 def PrepareBinhostUploads(input_proto, output_proto, config):
   """Return a list of files to uplooad to the binhost.
@@ -114,6 +118,8 @@
   for upload_target in upload_targets:
     output_proto.upload_targets.add().path = upload_target.strip('/')
 
+
+@faux.all_empty
 @validate.require('uri', 'sysroot.path')
 @validate.exists('uploads_dir')
 def PrepareDevInstallBinhostUploads(input_proto, output_proto, config):
@@ -166,6 +172,8 @@
     output_proto.upload_targets.add().path = upload_target
   output_proto.upload_targets.add().path = 'Packages'
 
+
+@faux.all_empty
 @validate.require('build_target.name', 'key', 'uri')
 @validate.validation_complete
 def SetBinhost(input_proto, output_proto, _config):
@@ -197,6 +205,7 @@
                                                 private=private)
 
 
+@faux.all_empty
 @validate.require('overlay_type')
 @validate.is_in('overlay_type', _OVERLAY_TYPE_TO_NAME)
 @validate.validation_complete