use .example suffix for httpd ssl example files

> Files in the vhost repo config directory with '-example' suffixes
> are currently used as a prompt for our deployment system to find and
> process a matching '.ugly' config file from our '/data/servers/
> vhosts' path (and the deployment system errors if those '.ugly' files
> don't exist).

https://github.com/mysociety/Non-Site-Specific/issues/474