Add template module for service instance

For now we create a service instance by "image_uuid,flavor_id,management_network" of configuration file, once we want to change the image or network, we have to rewrite the configuration file, and reload config, this is not convenient for admin user.
So I want add a module named 'template' which contains "image_uuid,flavor_id,management_network" and resource type.For example, I create a template A(image:xxxx, flavor:2, network:xxxx) for loadbalancer, when we want to create a loadbalancer service, we chose the template A we created, then create the loadbalancer service, it will generate an instance with image/flavor/network included by the template A. If we want to change the image, we only need to modify the template A.