Alias "unicode" to "str" under Python 3

The six way of doing this is to replace all occurences of "unicode"
with "six.text_type". However, "unicode" is non-ambiguous and
(arguably) easier to read. Also, using it makes the patches smaller,
which should help with backporting.

Reviewed-By: Petr Viktorin <pviktori@redhat.com>

ipapython/ssh.py

@@ -28,6 +28,11 @@ import struct
 from hashlib import md5, sha1
 from hashlib import sha256  #pylint: disable=E0611
 
+import six
+
+if six.PY3:
+    unicode = str
+
 __all__ = ['SSHPublicKey']
 
 OPENSSH_BASE_REGEX = re.compile(r'^[\t ]*(?P<keytype>[^\x00\n\r]+?) [\t ]*(?P<key>[^\x00\n\r]+?)(?:[\t ]+(?P<comment>[^\x00\n\r]*?)[\t ]*)?$')