Upgrade devserver and shellserver roles to PHP 7.2

Summary:
PHP 7.2 reaches both FreeBSD and Debian Sid packages.

We can so migrate from PHP 7.1 to PHP 7.2 dev/shell servers.

Test Plan: dereckson

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1362