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.

Change-Id: I2669f51145fc6fbf20da831995acfa17e9291f66
Merge "update autoscaling example with floating ip for lb pool"