Refactor Zemke-Rhyne pillar

Summary:
Zemke-Rhyne clients are now configured in the same file
than the credentials mapping.

Fixes T1670.

Test Plan: Deploy on Ysul

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1670

Differential Revision: https://devcentral.nasqueron.org/D2448