test: Silence unexpected message about failed VNC connection

Stopping the VM while the console page is open also severs the
connection to the VNC port (as the VNC server is going down). Ignore the
corresponding error message.

test/check-machines-consoles

@@ -146,6 +146,7 @@ class TestMachinesConsoles(VirtualMachinesCase):
                                     ".*Connection reset by peer")
         self.allow_browser_errors("Disconnection timed out.")
         self.allow_journal_messages(".* couldn't shutdown fd: Transport endpoint is not connected")
+        self.allow_journal_messages("127.0.0.1:5900: couldn't read: Connection refused")
 
     def testSwitchConsoleFromSerialToGraphical(self):
         b = self.browser