buffet: Use command schema to define "progress"

According to the GCD specification command progress is dictionary,
defined same way as parameters and results.
Mapping between "done" and "progress" dictionary is not obvious, so patch
removes updates of progress from CommandInstance::Done().

BUG=brillo:915
TEST=FEATURES=test emerge-gizmo buffet

Change-Id: If6f6d52dbc0595a8f1cf0cf949a741675c9e5f3c
Reviewed-on: https://chromium-review.googlesource.com/268352
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>

buffet/device_registration_info_unittest.cc

diff --git a/buffet/device_registration_info_unittest.cc b/buffet/device_registration_info_unittest.cc
index c833e5e..6e3feb2 100644
--- a/buffet/device_registration_info_unittest.cc
+++ b/buffet/device_registration_info_unittest.cc
@@ -566,7 +566,9 @@
                          chromeos::http::request_type::kPatch,
                          base::Bind(update_command_progress));
 
-  command->SetProgress(18);
+  native_types::Object progress{
+      {"progress", unittests::make_int_prop_value(18)}};
+  command->SetProgress(progress);
 
   // UpdateCommand when changing command status.
   auto update_command_state = [](const ServerRequest& request,