Fix openSuSE networking

During testing your openSuSE image from the vagrant cloud I noticed some problems when I defined multiple networks in the Vagrantfile. This is my attempt to fix them ;)

- Vagrant expects the interfaces to be named eth[0-9], which OpenSuSE, Fedora and possibly other distributions don't do in their current versions
- Therefore, you tried deleting /etc/udev/rules.d/70-persistent-net.rules, which is unfortunately not helping.
I also needed to symlink /dev/null to /etc/udev/rules.d/80-net-name-slot.rules.
- This in turn creates a new problem: eth0 has no configuration and systemd will continue trying to bring up enp0s3. To fix this, I moved the "network-hack" into the chroot script section of AutoYaST so that it is executed before YaST configures the interfaces.
- This requires specifying that eth0 should use dhcp
- What's left is that for some reason the default policy for new network interfaces is set to "on-cable-plug", which requires ifplugd. Otherwise, vagrant will fail to bring up the additional interfaces.