fix error namespace for ComponentXMPP

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

Fixes #3476
Fixes #3474

tests/test_stream_xep_0066.py

@@ -6,9 +6,6 @@ from slixmpp.test import SlixTest
 
 class TestOOB(SlixTest):
 
-    def tearDown(self):
-        self.stream_close()
-
     def testSendOOB(self):
         """Test sending an OOB transfer request."""
         self.stream_start(plugins=['xep_0066', 'xep_0030'])