Conditionally declare packages

To avoid potential "duplicate resource definitions", wrap package declarations in a conditional block.
Allow the `php-fpm` service name to be configured

Currently, the package name for `php-fpm` can be configured but the service name cannot.
Ensure that the `fpm_pool_dir` exists

Some PHP packages won't create this directory. It is safer to ensure that it exists.
Provide a better default for the CLI configuration file

On Debian systems, the configuration file for the CLI SAPI is located at `/etc/php5/cli/php.ini`.