CBQE-0: python 2.6 doesn't support assertRaise

Change-Id: I824b7e463775fad49ee5e495ee056b70724f05ee
Reviewed-on: http://review.couchbase.org/30947
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>