permission plugin: Auto-add operational atttributes to read permissions

The attributes entryusn, createtimestamp, and modifytimestamp
should be readable whenever thir entry is, i.e. when we allow reading
the objectclass.
Automatically add them to every read permission that includes objectclass.

https://fedorahosted.org/freeipa/ticket/4534

Reviewed-By: Martin Kosek <mkosek@redhat.com>

ipatests/test_xmlrpc/test_realmdomains_plugin.py

@@ -66,7 +66,8 @@ class test_realmdomains(Declarative):
                     objectclass=objectclasses.realmdomains,
                     aci=[
                         u'(targetattr = "associateddomain || cn || '
-                            u'objectclass")'
+                            u'createtimestamp || entryusn || '
+                            u'modifytimestamp || objectclass")'
                         u'(targetfilter = "(objectclass=domainrelatedobject)")'
                         u'(version 3.0;acl '
                             u'"permission:System: Read Realm Domains";'