sanlock: fix direct dump with offset
    
    For direct dump <path>:<offset>:<size> the dump is meant
    to continue reading/reporting for the entire range.  If
    the sector_size/align_size were not at <offset> the dump
    would stop.  Fix this by searching through the range for
    sector_size/align_size before beginning the real dump.
    
    Accept the M (MB) suffix on offset and size.
    
    Fix the printed offset of structures so that it is always
    relative to the start of the disk (it had been relative to
    the <offset>.)