Fix compatibility with gabbi >= 2.7.0

Fix the argument error caused by the change[1] in gabbi 2.7.0 .

[1] https://github.com/cdent/gabbi/commit/8511156559651ab0bf9d2679816d5a7818af290b

Change-Id: I936a3e6ddb0c254069839aaaa1f0eb7d4a72c85d
2 files changed