Description of problem:
Take advantage of the count_bytes iflag in dd in order to simplify ddWatchCopy (where we are currently maintaining our logic):

 def ddWatchCopy(src, dst, stop, size, offset=0):
     ...
     while left > 0:
         (iounit, count, iooffset) = _alignData(left, offset)
         ...
         cmd = [constants.EXT_DD, "if=%s" % src, "of=%s" % dst,
                "bs=%d" % iounit, "seek=%s" % iooffset, "skip=%s" % iooffset,
                "conv=%s" % conv, 'count=%s' % count]
         ...
         left = left % iounit
         offset = baseoffset + size - left