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/buffet_config.h b/buffet/buffet_config.h
index 0470755..6b73911 100644
--- a/buffet/buffet_config.h
+++ b/buffet/buffet_config.h
@@ -47,6 +47,15 @@
 
     ~Transaction();
 
+    void set_client_id(const std::string& id) { config_->client_id_ = id; }
+    void set_client_secret(const std::string& secret) {
+      config_->client_secret_ = secret;
+    }
+    void set_api_key(const std::string& key) { config_->api_key_ = key; }
+    void set_oauth_url(const std::string& url) { config_->oauth_url_ = url; }
+    void set_service_url(const std::string& url) {
+      config_->service_url_ = url;
+    }
     bool set_name(const std::string& name);
     void set_description(const std::string& description) {
       config_->description_ = description;