Usage:
vhd2rbd --vhd <vhd_file> --rbd <rbd_file> [-p] [-m] [-v] [-d]
rbd2vhd --rbd <rbd_file> --vhd <vhd_file> [--uuid <vdi_uuid>] [-p] [-m] [-v] [-d]
rbd2raw --rbd <rbd_file> --raw <raw_file> [-p] [-m] [-v] [-d]
rbd2nbd --rbd <rbd_file> --nbd <nbd_server> [-p] [-m] [-v] [-d]