For idempotence we need to run all apt-related tasks, like editing source files, adding keys, installing packages, etc, when running the 'packages' tag.
Debian 8 and Ubuntu 16.04 use PHP 5.6 and 7.0, respectively, and the php-fpm versions use slightly different configs and service names.
In Ubuntu 16.04 the package is now called just "php-fpm" and it makes more sense to just have this role be called that.