Use --data-dev or --data-dir for ceph-disk parameters to avoid making di...

ceph-disk parameters "--data-dev" or "--data-dir" are useful to avoid making directories such as /dev/sdc my mistake when you want to use a device that does not exist.
I believe the you can still specify `$DISK` as `/dev/sdb` and `ceph-disk` will detect if it is a device or not, falling back to creating a directory if that is the case