connection_exerciser::get_current_reading needs Amp calculation updated

[wes-b]

tests/Utilities/ConnEx/ConnEx.cpp connection_exerciser::get_current_reading() needs to be updated to properly calculate the measured current.

From Matt:

The original author noticed that if the number was negative, it was really 1000 + the value. So if the value was -2.98A, then the number was 1298. 2,98A would be 298. If a number was 1000 or greater, they would set the current to 1000 - current. This is correct, As 1000 - 1298 would give up -298.

The only small bug here is if the connection exerciser returns "negative zero" (1000). In that case we'd report 10 Amps, when we should report 0 amps. We just need to change if (raw_value > 1000) to if (raw_value >= 1000). I made the suggestion in the code.