Don't install software in the core role
Core is about configure a server, not about installing stuff.
We want to avoid to install software on containers OS.
Ensure this is no-op:
salt eglide state.apply roles/webserver-core/letsencrypt
Reviewed By: dereckson
Maniphest Tasks: T1259
Differential Revision: https://devcentral.nasqueron.org/D1064