This allows us to boot from an externally maintained rootfs, which is loaded from a given URL, and install this rootfs either on a tmpfs (RAM) or on a KVM (/dev/vda) block-device.
Sets up the rootfs, mounts required pseudo filesystems and calls /bin/switch_root on the new root.
Note that this also provisions a serial console upstart script if a serial console is passed as a kernel-argument.
The following kernel-arguments are supported:
- console=ttyS0
- ip=dhcp
- todisk=label
- size=size of tmpfs
- rootfs=url
- break=top|preunpack|bottom