'PUT /api/workflows/{workflow_id}/invocations/{invocation_id}/steps/{step_id}
Update state of running workflow step invocation - still very nebulous
but this would be for stuff like confirming paused steps can proceed
etc....
:param  workflow_id:      the workflow id (required)
:type   workflow_id:      str
:param  invocation_id:      the usage id (required)
:type   invocation_id:      str
:param  step_id:      encoded id of the WorkflowInvocationStep (required)
:type   step_id:      str
:raises: exceptions.MessageException, exceptions.ObjectNotFound'

@expose_api
def update_invocation_step(self, trans, workflow_id, invocation_id, step_id, payload, **kwd):

    decoded_invocation_step_id = self.decode_id(step_id)
    action = payload.get('action', None)
    invocation_step = self.workflow_manager.update_invocation_step(trans, decoded_invocation_step_id, action=action)
    return self.__encode_invocation_step(trans, invocation_step)
