ntp/client,packages_installed,packages_removed,etc_hosts: add validations and descriptions
nologin: add validations and descriptions
config_resolver: add validations and descriptions; add comment to resolv.conf file
motd: add validations and descriptions
set_hostname: add validations and descriptions
sysctl: add validations and descriptions
syslog: add validations and descriptions
tzconfig: add validations and descriptions
etc_hosts: report only when verbose
Add cfengine: 3.6.0 requirement to all sixified sketches
motd: fix os depends