XEP-0223: fix node standalone configuration (fixes #3555)

also add a stream test for that

tests/test_stream_xep_0223.py

@@ -0,0 +1,28 @@
+import unittest
+from slixmpp.test import SlixTest
+
+
+class TestPrivatePEP(SlixTest):
+
+    def testConfigureNode(self):
+        self.stream_start(mode='client', plugins=['xep_0223'])
+
+        self.xmpp.plugin['xep_0223'].configure(node="toto")
+        self.send("""
+<iq type="set" id="1">
+  <pubsub xmlns='http://jabber.org/protocol/pubsub#owner'>
+    <configure node='toto'>
+      <x xmlns='jabber:x:data' type='submit'>
+        <field var='FORM_TYPE' type='hidden'>
+          <value>http://jabber.org/protocol/pubsub#node_config</value>
+        </field>
+        <field var='pubsub#persist_items'><value>1</value></field>
+        <field var='pubsub#access_model'><value>whitelist</value></field>
+      </x>
+    </configure>
+  </pubsub>
+</iq>
+        """)
+
+
+suite = unittest.TestLoader().loadTestsFromTestCase(TestPrivatePEP)