MotionControlAction: Actions can be set only once

In the step class function of MotionControlAction (base for several actions), the initial flag control_strategy_set_ is never reset. As a consequence, the environment cannot be informed about a new control strategy of the same type.

    if (!control_strategy_set_)
    {
      action_.SetControlStrategy();
      control_strategy_set_ = true;
    }

This is not the same, but also related to #13