packer: apply predictable network interface workaround for Debian/stretch and newer

We currently get a default network configuration in
/etc/network/interfaces which refers to eth0 (and eth1). But on
Debian/stretch and newer the devices follow the new network
interface naming schema (see udev's README.Debian for further
details). This causes e.g. a vagrant up run for a stretch based
base box to fail since it can't login via SSH then. Until there's
a better approach available just use the predictable network
interface naming schema via udev as recommended.