ceph-disk: blacklist /dev/fd0

    blkid -s TYPE /dev/fd0 has been verified to hang forever on a
    H8DMR-82 supermicro motherboard running
    
    3.8.0-33-generic #48~precise1-Ubuntu SMP Thu Oct 24 16:28:06 UTC 2013
    x86_64
    
    It is unlikely that ceph will ever be used on floppy disks, they
    can be blacklisted.
    
    http://tracker.ceph.com/issues/6827 fixes: #6827
    
    Signed-off-by: Loic Dachary <loic@dachary.org>