Misnamed variable in behavior.py

In line 942 of behavior.py the variable `connection.CONTROL_PRIORITY_LEVEL.RESERVE_CONTROL`  does not exist.  The executable `anki_vector.reserve_control` and function `anki_vector.behavior.ReserveBehaviorControl()` fail with an exception, but run correctly if `connection.ControlPriorityLevel.RESERVE_CONTROL` is substituted.