Added proxy_set_header and vhost_cfg_prepend to the ssl vhost template.

proxy_set_header and vhost_cfg_prepend was missing from ssl vhost template.

proxy_set_header is important in cases where nginx is used as a SSL proxy and the backend application need
to have custom headers appended to.

For instance Wordpress need headers like 'X-Forwarded-Proto https' to work properly with SSL proxying.