Convert zr state to a proper unit

Summary:
Repository convention requires a role is a set of units,
but the webserver-legacy roles contained a zr.sls state,
with a files/ folder directly in the role.

This change moves the zr content to a zr unit.

Test Plan: no op

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1296