ipalib.aci: Port to Python 3
    
    - Don't encode under Python 3, where shlex would choke on bytes
    - Sort the attrs dictionary in export_to_string, so the tests are
      deterministic. (The iteration order of dicts was always unspecified,
      but was always the same in practice under CPython 2.)
    
    Reviewed-By: Tomas Babej <tbabej@redhat.com>