Add nologin sketch

Adds sketch to prevent non privledged users from logging into the
system. Facilities for all users (/etc/nologin) and individual users
(nologin shell) are provided as seperate entry points. Regenerated
cfsketches.json
Merge pull request #422 from nickanderson/security/etc_nologin

Add nologin sketch Adds sketch to prevent non privledged users from logging into the system. Facilities for all users (/etc/nologin) and individual users (nologin shell) are provided as seperate entry points.