Replace six.iteritems() with .items()

1.As mentioned in [1], we should avoid using
six.iteritems to achieve iterators. We can
use dict.items instead, as it will return
iterators in PY3 as well. And dict.items/keys
will more readable. 2.In py2, the performance
about list should be negligible, see the link [2].
[1] https://wiki.openstack.org/wiki/Python3
[2] http://lists.openstack.org/pipermail/openstack-dev/2015-June/066391.html

Change-Id: I8b1e3dd75c700c3c2d41223309cd6c3af1ebdddc

oslo_config/cfg.py

@@ -2156,7 +2156,7 @@ class _CachedArgumentParser(argparse.ArgumentParser):
         # not touch positional. For the reason optional opts go first in
         # the values we only need to find an index of the first positional
         # option and then sort the values slice.
-        for container, values in six.iteritems(self._args_cache):
+        for container, values in self._args_cache.items():
             index = 0
             has_positional = False
             for index, argument in enumerate(values):

oslo_config/fixture.py

@@ -16,7 +16,6 @@
 #    under the License.
 
 import fixtures
-import six
 
 from oslo_config import cfg
 
@@ -70,7 +69,7 @@ class Config(fixtures.Fixture):
 
         group = kw.pop('group', None)
         enforce_type = kw.pop('enforce_type', False)
-        for k, v in six.iteritems(kw):
+        for k, v in kw.items():
             self.conf.set_override(k, v, group, enforce_type=enforce_type)
 
     def _unregister_config_opts(self):
@@ -174,7 +173,7 @@ class Config(fixtures.Fixture):
 
         raw_config = dict()
         raw_config[group] = dict()
-        for key, value in six.iteritems(kwargs):
+        for key, value in kwargs.items():
             # Parsed values are an array of raw strings.
             raw_config[group][key] = [str(value)]