Replace six.iteritems() with .items()

We should avoid using six.iteritems/keys achieve iterators. We can use
dict.items/keys instead, as it wil l return iterators in PY3 as well.
And dict.items/keys will more readable.

In py2, the performance about list should be negligible, see
https://wiki.openstack.org/wiki/Python3 and
http://lists.openstack.org/pipermail/openstack-dev/2015-June/066391.html

Change-Id: I6f8ee2ed36ed94e2ef8347463f56eed44464a605

bifrost/inventory.py

@@ -114,7 +114,6 @@ intended to support specific host queries.
 import csv
 import json
 import os
-import six
 import sys
 import yaml
 
@@ -329,7 +328,7 @@ def _process_shade(groups, hostvars):
         else:
             name = machine['name']
         new_machine = {}
-        for key, value in six.iteritems(machine):
+        for key, value in machine.items():
             # NOTE(TheJulia): We don't want to pass infomrational links
             # nor do we want to pass links about the ports since they
             # are API endpoint URLs.

playbooks/library/os_ironic_facts.py

@@ -22,8 +22,6 @@ try:
 except ImportError:
     HAS_SHADE = False
 
-import six
-
 DOCUMENTATION = '''
 ---
 module: os_ironic_facts
@@ -117,7 +115,7 @@ def main():
             new_driver_info = dict()
             # Rebuild driver_info to remove any password values
             # as they will be masked.
-            for key, value in six.iteritems(facts['driver_info']):
+            for key, value in facts['driver_info'].items():
                 if 'password' not in key:
                     new_driver_info[key] = value
             if new_driver_info: