UTF-8 environment

Summary:
Some PHP application requires to run CLI commands. It would be more
convenient if the container environment is full UTF-8.

Fixes T669.

Test Plan:
Build a new container for DevCentral
and see how Drydock repository automation behaves.

To test UTF-8 environment propagation :

$ mkdir /tmp/phpinfo
$ cd /tmp/phpinfo
$ cat > index.php
<?php phpinfo(32);
^D
$ docker run -d -v /tmp/phpinfo:/var/wwwroot/default -p 8080:80 nasqueron/nginx-php-fpm

Reviewers: Kaliiixx

Subscribers: Nasqueron Docker deployment squad

Projects: Docker images

Maniphest Tasks: T669

Differential Revision: http://devcentral.nasqueron.org/D245