Bump PHP version for devserver and shellserver roles

Summary:
Ideally, we would like 7.4 everywhere. That's ok for FreeBSD.

On Debian Sid, through the package system, only PHP 7.3 is available.
So we currently bump to PHP 7.3. If someone needs PHP 7.4 on Eglide,
we can use the builder PHP unit to prepare a custom build or we can
use the https://deb.sury.org/ repository to provide it.

Reference: https://www.php.net/releases/7_4_0.php

Test Plan: php -i on WindRiver

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2117