Fixes #3995 - Add backup of /etc/{init.d,default,cron.d}/rudder-agent in preinst and restore action in check-rudder-agent cron file

Fixes #3995 - Add backup of /etc/{init.d,default,cron.d}/rudder-agent in preinst and restore action in check-rudder-agent cron file


See http://www.rudder-project.org/redmine/issues/3995