nginx/Dockerfile.template: Add auth_request to NGINX_MODULES_HTTP
nginx/Dockerfile.template: Add auth_request to NGINX_MODULES_HTTP

This module is simple and flexible [1].  I'm pushing it for the new
docker-registry auth, so I'm going to install it by default in my
Nginx image.

[1]: http://nginx.org/en/docs/http/ngx_http_auth_request_module.html

ostree/dockerfile,wking/dockerfile,fr34k8/dockerfile