Exit Code Propagation

[fridayy]

Description

This PR adds the "Exit Code Propagation" behavior as discussed here.

The exit/1 function now checks if the given error is an exec.ExitError. If so the exit code wrapped in the exec.ExitError is propagated back to the caller otherwise the catch all 1 exit code is used.

Implementing this in exit/1 means that this change is applied in a broader context and not only for "RUN" commands as described in the issue. I thought that might be more consistent and I hope you do share my opinion.

I added a quick integration test case to verify the wanted behavior. As I am fairly inexperienced with go (and its error handling semantics) I am happy to hear your feedback. :)

Have a nice day!

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Adds integration tests if needed.

See the contribution guide for more details.

Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

Release Notes

The kaniko executor now propagates exit codes of failing commands back to the caller instead of exiting with error code 1.

Dockerfile:

FROM python:3.7

RUN exit 123

CMD ["python", "--version"]

When trying to build the given Containerfile kaniko will exit with the exit code 123.