Assign explicitly webserver-legacy role to Ysul

Summary:
Servers will receive wwwroot folder build instructions filtered
by roles. Roles should then be explicitely declared to the nodes
pillar entry, so node.filter_by_role don't forget anything.

Ref T1325

Test Plan: salt-call --local node.filter_by_role web_content_sls

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1325

Differential Revision: https://devcentral.nasqueron.org/D1258