Add notification to composer LWRP

Complies with FC017
Cover all supported platforms in attributes

Complies with FC024
Exclude foodcritic rule for using curl in an execute resource

Downloading the installer script for Composer triggers rule FC041, but
I think it's actually a valid use case here.
Set up common service resource for php-fpm

This way we can have other chef resources reload php-fpm, using a
common service name
Convert php_fpm_pool definition to an LWRP

Complies with FC015
Take out process.priority from config

This only seems to be compatible with version >5.4. It prevents php-fpm
from starting on older versions. We could re-enable it later, but it
has to be conditional.