Switch dereckson shell to tcsh on Eglide

Summary:
We introduce in our users dictionary a new shell parameter.

As a follow-up, we should create a function to map bash, tcsh, etc.
according the OS, so we can only write tcsh in the dictionary.

Test Plan:

$ grep dereckson /etc/passwd
dereckson:x:5001:5001:Sebastien Santoro,,,:/home/dereckson:/bin/bash

$ grep dereckson /etc/passwd
dereckson:x:5001:5001:Sebastien Santoro,,,:/home/dereckson:/usr/bin/tcsh

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D827