privetd: Implement privet/v3/commands/status

Privetd just forwards IDs to the buffet and buffet returns JSON
representation of the command.

BUG=brillo:430
TEST=unittest

Change-Id: I5698f9fc915ae32dc2b9be3cc35f8efe919ee4e3
Reviewed-on: https://chromium-review.googlesource.com/261641
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/manager.h b/buffet/manager.h
index d307ca2..d61c6fa 100644
--- a/buffet/manager.h
+++ b/buffet/manager.h
@@ -70,6 +70,9 @@
   // Handles calls to org.chromium.Buffet.Manager.AddCommand().
   void AddCommand(DBusMethodResponse<> response,
                   const std::string& json_command) override;
+  // Handles calls to org.chromium.Buffet.Manager.GetCommand().
+  void GetCommand(DBusMethodResponse<std::string> response,
+                  const std::string& id) override;
   // Handles calls to org.chromium.Buffet.Manager.Test()
   std::string TestMethod(const std::string& message) override;