public static void AddRole(this IServiceManagement proxy,
                            string subscriptionId,
                            string serviceName,
                            string deploymentName,
                            PersistentVMRole role)
 {
     proxy.EndAddRole(
         proxy.BeginAddRole(subscriptionId,
                            serviceName,
                            deploymentName,
                            role,
                            null,
                            null));
 }