Use Python3-compatible dict method names

Python 2 has keys()/values()/items(), which return lists,
iterkeys()/itervalues()/iteritems(), which return iterators,
and viewkeys()/viewvalues()/viewitems() which return views.

Python 3 has only keys()/values()/items(), which return views.
To get iterators, one can use iter() or a for loop/comprehension;
for lists there's the list() constructor.

When iterating through the entire dict, without modifying the dict,
 the difference between Python 2's items() and iteritems() is
negligible, especially on small dicts (the main overhead is
extra memory, not CPU time). In the interest of simpler code,
this patch changes many instances of iteritems() to items(),
iterkeys() to keys() etc.

In other cases, helpers like six.itervalues are used.

Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipaplatform/base/services.py

@@ -28,6 +28,8 @@ import json
 import time
 import collections
 
+import six
+
 import ipalib
 from ipapython import ipautil
 from ipaplatform.paths import paths
@@ -78,7 +80,7 @@ class KnownServices(collections.Mapping):
         return len(self.__d)
 
     def __call__(self):
-        return self.__d.itervalues()
+        return six.itervalues(self.__d)
 
     def __getattr__(self, name):
         try: