Return standard human-friendly UUID.

def bytes2uuid(b):
    """ Return standard human-friendly UUID. """
    if b.strip(chr(0)) == '':
        return None

    s = b.encode('hex')
    return "%s-%s-%s-%s-%s" % (s[0:8], s[8:12], s[12:16], s[16:20], s[20:])