Fix/use pwr aux

[calbaker]

• all instances of solve_step set pwr_aux
• pwr_aux is always set, regardless of whether the locomotive is moving or not
• TODO: maybe implement some fancier control logic that can selectively turn off locomotives

[SWRIganderson]

@calbaker

I'm looking at aux calcs this morning. I think we already have something in there for if the engine is on for the conventional. It looks at if the engine is running. This is the correct way of doing. If the engine is running, you will have cooling fan loads, maybe air compressor, AC, heater, controllers, lights,....... This will also be true for a BEL, but I'm not sure exactly how you specify the equivalent of on or off. One of the big take aways in the ZANZEFF work was the aux loads were really important when sitting still.

[calbaker]

@SWRIganderson, I'm thinking it would be good for both of us to dig into this a bit to make sure the way we're exposing engine on/off logic make sense.