[Libguestfs] Change to unstable mkfs-btrfs API

I'm going to change the mkfs-btrfs API so its single and only parameter is a list of devices (instead of a single device). btrfs filesystems can span multiple devices, so this is necessary to create such filesystems, eg: mkfs-btrfs ["/dev/vda1", "/dev/vdb1"] mount "/dev/vda1", "/" would create a filesystem across two devices and mount it. Note this changes the API, but this API has not yet been released in a stable version of libguestfs, so we're allowed to do this. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into Xen guests. http://et.redhat.com/~rjones/virt-p2v