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>

ipalib/plugins/idviews.py

@@ -19,6 +19,8 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 import re
 
+import six
+
 from ipalib.plugins.baseldap import (LDAPQuery, LDAPObject, LDAPCreate,
                                      LDAPDelete, LDAPUpdate, LDAPSearch,
                                      LDAPRetrieve, global_output_params)
@@ -31,6 +33,9 @@ from ipalib.util import (normalize_sshpubkey, validate_sshpubkey,
 
 from ipapython.dn import DN
 
+if six.PY3:
+    unicode = str
+
 _dcerpc_bindings_installed = False
 
 if api.env.in_server and api.env.context in ['lite', 'server']: