Remove WordPress environmental variables from global environment

PHP-FPM starts with a clean environment, negating any environmental variables that are set outside of the service startup process. This pull request takes the `wordpress_env` environmental variable mapping and passes it to `php_fpm_env` so that processes under PHP-FPM can have access to the proper environmental variable values.

This snuck by in my previous tests because the default `wp-config-sample.php` works out of the box with the default database name, username, and password I chose.