Add missing tunnel on new class

lib/private/systemconfig.php

@@ -28,6 +28,14 @@ namespace OC;
  * fixes cyclic DI: AllConfig needs AppConfig needs Database needs AllConfig
  */
 class SystemConfig {
+	/**
+	 * Lists all available config keys
+	 * @return array an array of key names
+	 */
+	public function getKeys() {
+		return \OC_Config::getKeys();
+	}
+
 	/**
 	 * Sets a new system wide value
 	 *