Replace a use of then_call with addCallback and return connector from teardown_connector.
Replace a use of then_call with addCallback and return connector from teardown_connector.

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