Py3: Replace six.moves imports

Replace six.moves and six.StringIO/BytesIO imports with cannonical
Python 3 packages.

Note: six.moves.input behaves differently than builtin input function.
Therefore I left six.moves.input for now.

See: https://pagure.io/freeipa/issue/7715
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>

daemons/ipa-otpd/test.py

@@ -19,12 +19,11 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from io import StringIO
 import struct
 import subprocess
 import sys
 
-from six import StringIO
-
 try:
     from pyrad import packet
     from pyrad.dictionary import Dictionary