Fixes #4466: add detect_os.sh script

[VinceMacBuche]

http://www.rudder-project.org/redmine/issues/4466

Not finished yet, an error with missing perl-5.12.4.tar.gz file occurs here

[jooooooon]

This is an over-simplified view of this change.

The detect-os.sh file comes from an internal repository that we use to build packages (it is internal because it contains SSH keys and hostnames to our internal IT infrastructure). Clearly, the detect-os.sh file should be in the public rudder-packages repository, not in there.

But we can't just go around duplicating code, and making this work for one package! That file is used in all package builds. If we add it here, we must remove it from the internal packaging repo (DRY is not just a buzz word, it's what we do, without exception).

Please rework this, including the internal packaging repo in your considerations.

[Kegeruneku]

Creating another PR using this one. See ticket.