The new DO images have a different label causing DO images to not boot
root@ubuntu-2gb-sfo1-01:~# e2label /dev/vda1
cloudimg-rootfs
net.ifnames=0 is used get unpredictable names as per
https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/.
Not sure why we want that.
Not sure about notsc and clocksource.
This change also preserves any existing cmdline