And modify the tests to work, by adding the <x/> node in all join presences

tests/end_to_end/scenarios/not_connected_error.py

@@ -6,7 +6,7 @@ scenario = (
     send_stanza("<presence type='unavailable' from='{jid_one}/{resource_one}' to='#foo%{irc_server_one}/{nick_one}' />"),
     # Fixme: what is the purpose of this test? Check that we don’t receive anything here…?
 
-    send_stanza("<presence from='{jid_one}/{resource_one}' to='#foo%{irc_server_one}/{nick_one}' />"),
+    send_stanza("<presence from='{jid_one}/{resource_one}' to='#foo%{irc_server_one}/{nick_one}' ><x xmlns='http://jabber.org/protocol/muc'/></presence>"),
     sequences.connection(),
     expect_self_join_presence(jid='{jid_one}/{resource_one}', chan="#foo", nick="{nick_one}"),
 )