Make php-fpm default to serving on Unix sockets instead of TCP

[gregharvey]

This is actually more complicated than I realised, effectively we want ce-provision to default to using a Unix socket instead of TCP/IP (as it currently does) because we rarely actually have a PHP server cluster, usually PHP is on the same machine as the web server, so losing a load of performance to TCP/IP makes no sense in many cases. That being said, we still want to support TCP/IP, and this impacts NGINX and Apache configs, as they need to handle the config from the PHP-FPM role.

There's some incomplete WIP against the 1.x branch here, which can be used as inspiration but probably won't cleanly merge to 2.x any more:

• https://github.com/codeenigma/ce-provision/pull/860/files