Andrey, 

Let me complete the stack trace:


Task is:                                                                                                                                                                                                           
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  KeystoneBasic.authenticate_user_and_validate_token:                                                                                                                                                              
    -                                                                                                                                                                                                              
      runner:                                                                                                                                                                                                      
        type: "constant_for_duration"                                                                                                                                                                              
        duration: 100                                                                                                                                                                                              
        concurrency: 1                                                                                                                                                                                             
                                                                                                                                                                                                                   
Task syntax is correct :)                                                                                                                                                                                          
Running Rally version 1.1.0                                                                                                                                                                                        
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Task  644fde0c-82a4-46e0-9d7d-c2082bd71f8f: started                                                                                                                                                                
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Running Task... This can take a while...                                                                                                                                                                           
                                                                                                                                                                                                                   
To track task status use:                                                                                                                                                                                          
                                                                                                                                                                                                                   
        rally task status                                                                                                                                                                                          
        or                                                                                                                                                                                                         
        rally task detailed                                                                                                                                                                                        
                                                                                                                                                                                                                   
Using task: 644fde0c-82a4-46e0-9d7d-c2082bd71f8f                                                                                                                                                                   
2018-10-29 15:41:36.320 1 INFO rally.task.context [-] Task 644fde0c-82a4-46e0-9d7d-c2082bd71f8f | Context admin_cleanup@openstack cleanup() started                                                                
2018-10-29 15:41:39.914 1 INFO rally.task.context [-] Task 644fde0c-82a4-46e0-9d7d-c2082bd71f8f | Context admin_cleanup@openstack cleanup() finished in 3.59 sec                                                   
2018-10-29 15:41:39.914 1 INFO rally.task.context [-] Task 644fde0c-82a4-46e0-9d7d-c2082bd71f8f | Context users@openstack cleanup() started                                                                        
2018-10-29 15:41:43.476 1 INFO rally.task.context [-] Task 644fde0c-82a4-46e0-9d7d-c2082bd71f8f | Context users@openstack cleanup() finished in 3.56 sec                                                           
2018-10-29 15:41:43.891 1 INFO rally.task.engine [-] Load duration is: 0.0                                                                                                                                         
2018-10-29 15:41:43.891 1 INFO rally.task.engine [-] Full runner duration is: 0.0                                                                                                                                  
2018-10-29 15:41:43.892 1 INFO rally.task.engine [-] Full duration is: 9.6213                                                                                                                                      
2018-10-29 15:41:43.903 1 ERROR rally.task.engine [-] Unexpected exception during the workload execution: TypeError: 'NoneType' object is not callable
2018-10-29 15:41:43.903 1 ERROR rally.task.engine Traceback (most recent call last):
2018-10-29 15:41:43.903 1 ERROR rally.task.engine   File "/usr/local/lib/python2.7/dist-packages/rally/task/engine.py", line 509, in _run_workload
2018-10-29 15:41:43.903 1 ERROR rally.task.engine     workload["args"])
2018-10-29 15:41:43.903 1 ERROR rally.task.engine   File "/usr/local/lib/python2.7/dist-packages/rally/task/runner.py", line 168, in run
2018-10-29 15:41:43.903 1 ERROR rally.task.engine     self._run_scenario(scenario_plugin, "run", context, args)
2018-10-29 15:41:43.903 1 ERROR rally.task.engine   File "/usr/local/lib/python2.7/dist-packages/rally/plugins/common/runners/constant.py", line 335, in _run_scenario
2018-10-29 15:41:43.903 1 ERROR rally.task.engine     result = iter_result.next(timeout)
2018-10-29 15:41:43.903 1 ERROR rally.task.engine   File "/usr/lib/python2.7/multiprocessing/pool.py", line 668, in next
2018-10-29 15:41:43.903 1 ERROR rally.task.engine     raise value
2018-10-29 15:41:43.903 1 ERROR rally.task.engine TypeError: 'NoneType' object is not callable
2018-10-29 15:41:43.903 1 ERROR rally.task.engine
2018-10-29 15:41:43.926 1 INFO rally.task.engine [-] Task 644fde0c-82a4-46e0-9d7d-c2082bd71f8f | Completed: Running task.