test_carstate.py needs quick update for OP .4

[Reyuuk]

The current version of OP is incompatible with test_carstate.py. This script is still referencing CS.errors, which has been renamed to CS.events in the rest of OP.

See lines 36 & 26 in https://github.com/commaai/openpilot/blob/devel/selfdrive/debug/test_carstate.py

Also, as an aside, I personally think that this code should also include PATH lines to make it easier to run tests without having to mess with python paths. Adding the below would allow us to run the test with a simple: "python test_carstate.py" - if there's a good reason not to add these imports, feel free to ignore.

import sys
sys.path.append('/data/openpilot')