Move back the fish installation to shellserver role

Summary:
Commit f91421e8edad has moved shells provisionning
from shellserver to core role.

The list of shell contains fish, not available in CentOS 7
core list of packages, it requires EPEL.

Test Plan: Reapply userland unit on Equatower

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1399