Enable Version module on Debian

Tested on Squeeze & Precise, same output:

    Notice: /Stage[main]/Apache::Config/Exec[enable-version]/returns: executed successfully
    Info: /Stage[main]/Apache::Config/Exec[enable-version]: Scheduling refresh of Service[apache2]

Instance is usable after the installer is done.

Not tested Wheezy yet (still need to get an Openstack image for that :P) but otherwise it seems to work safely.