Print MOTD through OpenSSH when needed

Summary:
This change introduces in the Jinja2 map a new capabilities
dictionary to explain what an OS/distribution does or doesn't not.

PrintMotd will be set at yes or no according the MOTD-printed-at-login
capability.

Test Plan: Ensure Debian receives a PrintMotd no, and FreeBSD a PrintMotd yes.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1130