gfs2_convert: remember number of blocks when converting quotas
    
    This patch changes function copy_quotas so that it properly copies
    the di_blocks field from the GFS1 quotas file to its new GFS2 file.
    If the quota file had a non-trivial size, gfs2_convert was copying
    all the data and pointers, but not properly setting the di_blocks.
    This ordinarily isn't tragic because the file is never deleted, but
    it did flag fsck.gfs2 errors.
    
    rhbz#887374