We just need the target platform version in the template

Rework the version check to be on the safe side for a future SP4 update for
SLES 11.
Use systemctl on SLES12 to enable chef-client
SLES12 uses a different mechanism to enable/diable core dumps
Set hostname in autoyast network config

This seems to be needed on SLES12, otherwise the hostname is not configured
correctly when crowbar_join.sh is running.