Pass `nginx_config` variable to cloud_formation
Pass `nginx_config` variable to cloud_formation

This sets `live_config` as the default value for cloud formation
templates so that they don't break with the new data in the playbooks.

We can change this to a variable if we decide we want to be able to
activate maintenance mode in this way.

alphagov/digitalmarketplace-aws,alphagov/digitalmarketplace-aws,alphagov/digitalmarketplace-aws