update autoscaling example with floating ip for lb pool

This patch updates autoscaling.yaml to (a) require an external_network_id parameter and (b) to allocate a floating ip address and associate it with the loadbalancer pool.

It adds a website_url output to make it consisent with some of the other Wordpress examples.

It is hard to find documentation on how to assign a floating ip address to a load balancer, so I thought this seemed like a good place for the example.