Fixes #3925: Prevent UUID removal when upgrading rudder-agent

* Add script to check UUID of Rudder and CFEngine process, and set 'root' to UUID only during rudder-server-root install but use the script during upgrade

* Add GPLv3 License to new script

* Fix typos and change name check_rudder-ganet to check-rudder-agent

* Remove changes and add comments on rudder-server-root package, Add temporary cron set into rudder-agent postinst and comments for check-rudder-agent

* Add comments in rudder-agent postinst

* Fix wrong files and bizarre logics

* Make sure that the cron fule added in this issue has correct permissions

Ticket: http://www.rudder-project.org/redmine/issues/3925

To be merged in 2.4 branch