fix error namespace for ComponentXMPP

in SlixTest, if mode=="component", restore
jabber:client namespace afterwards

Fixes #3476
Fixes #3474

tests/test_stream_presence.py

@@ -11,9 +11,6 @@ class TestStreamPresence(SlixTest):
     def setUp(self):
         self.stream_start(jid='tester@localhost', plugins=[])
 
-    def tearDown(self):
-        self.stream_close()
-
     def testInitialUnavailablePresences(self):
         """
         Test receiving unavailable presences from JIDs that