this adds the functions for listing the disks (mostly copied from
the ceph code), checking if a disk is a valid blockdevice, if it
is used/in a zfs pool/as an lvm pv, and an init function (just to add a gpt header;
this is important if one wants to use a fresh disk for ceph journals)
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
