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oslo project provide jsonutils, and mistralclient use it in many place[1], this PS to update the remained json module to oslo jsonutils for consistency. [1]: https://github.com/openstack/python-mistralclient/search?utf8=%E2%9C%93&q=jsonutils&type= Change-Id: Ibbb3f2b5636147a0faf7a23e6bb177978282cbd3