keystoneclient.utils [-] create takes at most 1 positional argument (2 given)

Run rally task start create-and-list-users.yaml,have a warning in the result:
2015-06-26 17:26:48.705 11878 WARNING keystoneclient.utils [-] create takes at most 1 positional argument (2 given)

How can pass to parameters?my env is keystone v3.

testcase file:
---
  KeystoneBasic.create_and_list_users:
    -
      args:
        name_length: 10

      runner:
        type: "constant"
        times: 1
        concurrency: 10