Debian 9 is still in beta and doesn't have nginx.org builds yet, so we need to use the nginx package in Debian's repositories, and that required a bit of a different configuration. After official nginx.org builds are released we can revert this.
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.