Replace .iteritems() with six.iteritems()

Replace .iteritems() with six.iteritems() everywhere except in
module_utils (because there's no 'six' on the remote host).  And except
in lib/ansible/galaxy/data/metadata_template.j2, because I'm not sure
six is available there.

contrib/inventory/collins.py

@@ -83,6 +83,8 @@ try:
 except ImportError:
     import simplejson as json
 
+from six import iteritems
+
 
 class CollinsDefaults(object):
     ASSETS_API_ENDPOINT = '%s/api/assets'
@@ -174,7 +176,7 @@ class CollinsInventory(object):
         # the CQL search feature as described here:
         # http://tumblr.github.io/collins/recipes.html
         attributes_query = [ '='.join(attr_pair)
-            for attr_pair in attributes.iteritems() ]
+            for attr_pair in iteritems(attributes) ]
         query_parameters = {
             'details': ['True'],
             'operation': [operation],