When building cloud images oz uses dracut to setup networking and it
in turn makes a ifcfg-en<something> file with this config. We don't
want to use this, we want to always use ifcfg-eth0 so it's the same
on all images. So, we remove ifcfg-en* (They are different on each
arch we make cloud images for, but en* gets them all).
Additionally we were using some old udev tricks to get eth0, but this
is error prone and already incorrect as systemd-udev has moved files
around, so instead we just switch to net.ifnames=0 on the boot line,
which should continue working.