CBQE-0: fix failUnlessRaises() takes ...

python version related

Change-Id: Ia1930cb050156470c1d6c18b5bfcf8c864ff2615
Reviewed-on: http://review.couchbase.org/30046
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>