fix: fail quickly if a subprocess returns 1

[sofisl]

In Python, os.system() executes a command in a subshell. While the command itself (like python3 owlbot.py) returns a non-zero exit code when it crashes, os.system() simply returns that value to the caller and continues execution of the script.

Because the main script (Step #5 in your logs) finished its loop without explicitly checking the return value of system() and calling sys.exit(1), Cloud Build marked Step #5 as "Finished" successfully.

other thing in this PR is adding a build script for dev purposes, you can run build.sh and test locally more easily