create version of the image with fpm

[jrobinsonc]

The actual image comes with apache by default and the idea is to create a version with php-fpm.

It could be in a different branch and could be defined as jrobinsonc/php:7.2-fpm.

This will allow child images to have fpm implemented:

• https://github.com/jrobinsonc/docker-drupal-image
• https://github.com/jrobinsonc/docker-laravel-image
• https://github.com/jrobinsonc/docker-wordpress-image