Now the json format which was exported by `rally task results` is too old,
We expect to use `rally task report --json` instead of it.
New json exporter command:
rally task report --json --uuid <task_uuid> --out <dest_file>
rally task export --uuid <task_uuid> --type json --to <dest_file>
Change-Id: Idbb20513ec1013d0f2b7a7458dc8bffef4771e84