config plugin: add a test ensuring EmptyModlist is returned

Add a test to test_config_plugin, that calls ipa config-mod
with the same value as already present in LDAP.
The call must return EmptyModlist.

Related: https://pagure.io/freeipa/issue/9063
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipatests/test_xmlrpc/test_config_plugin.py

@@ -312,4 +312,13 @@ class test_config(Declarative):
                 'value': None,
             },
         ),
+        dict(
+            desc='Set the value to the already set value, no modifications',
+            command=(
+                'config_mod', [], {
+                    'ipasearchrecordslimit': u'100',
+                },
+            ),
+            expected=errors.EmptyModlist(),
+        ),
     ]