`ThrusterAndKillBoardSimulation` should use Python 3 `bytes`, not `str` in Noetic

[cbrxyz]

The ThrusterAndKillBoardSimulation class likely supported operations with both str and bytes in Python 2 because of the similarities between the classes. Python 3 separates the classes quite a bit, and it appears the class may no longer be able to handle the bytes class in Python 3.