Revert "slapos/util: Skip testing on python3"

This reverts commit c251e941.

slapos/tests/test_util.py

@@ -31,7 +31,6 @@ import tempfile
 import unittest
 import shutil
 from pwd import getpwnam
-import six
 
 class TestUtil(unittest.TestCase):
   """
@@ -158,14 +157,12 @@ class TestUtil(unittest.TestCase):
     'none': 'None',
     'ukey': 'ustr'}
 
-  @unittest.skipIf(six.PY3, 'just not checked on python 3')
   def test_xml2dict(self):
     self.assertEqual(
       self.xml2dict_outdict,
       slapos.util.xml2dict(self.xml2dict_xml)
     )
 
-  @unittest.skipIf(six.PY3, 'just not checked on python 3')
   def test_dict2xml(self):
     self.assertEqual(
       self.xml2dict_xml,