Stub TestXMLStream's addObserver() too.
Stub TestXMLStream's addObserver() too.

Sending IQ stanzas expects this method.

vishwaprakashmishra/xmatrix,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,harrissoerja/vumi,TouK/vumi