buffet: Add D-Bus API to change GCD service settings

Added function UpdateServiceConfig that can be used to switch servers
for testing. Function modifies client_id, client_secret, api_key,
oauth_url and service_url.

BUG=brillo:1058
TEST='FEATURES=test emerge-gizmo buffet'

Change-Id: Ia8f8ba3ad57372ecedbff2819ce1991ba391a41d
Reviewed-on: https://chromium-review.googlesource.com/271387
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/manager.cc b/buffet/manager.cc
index 2002eb2..d21ec8b 100644
--- a/buffet/manager.cc
+++ b/buffet/manager.cc
@@ -243,6 +243,16 @@
                                         error);
 }
 
+bool Manager::UpdateServiceConfig(chromeos::ErrorPtr* error,
+                                  const std::string& client_id,
+                                  const std::string& client_secret,
+                                  const std::string& api_key,
+                                  const std::string& oauth_url,
+                                  const std::string& service_url) {
+  return device_info_->UpdateServiceConfig(client_id, client_secret, api_key,
+                                           oauth_url, service_url, error);
+}
+
 void Manager::OnCommandDefsChanged() {
   chromeos::ErrorPtr error;
   // Limit only to commands that are visible to the local clients.