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>

ipapython/ipautil.py

@@ -41,13 +41,13 @@ import grp
 from contextlib import contextmanager
 import locale
 import collections
+import urllib
 
 from dns import resolver, reversename
 from dns.exception import DNSException
 
 import six
 from six.moves import input
-from six.moves import urllib
 
 from ipapython.dn import DN