Return exit code 1 if warnings are given

[ClemensLinnhoff]

Reference to a related issue in the repository

#75

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Return exit code 1 if warnings are given, so CI pipelines recognize, that osi-validation found something.

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• My code and comments follow the contributors guidelines of this project.
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation for osi-validation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works. (Positive test in the pipeline when running the application)
• New and existing unit tests / travis ci pass locally with my changes.

[ClemensLinnhoff]

@jdsika, of course giving an exit code will cause the pipeline to fail here. How should we handle this?

We could change the test trace file to not generate warnings. But I actually like showing this as an example. Alternatively we could catch the exit code and make the pipeline pass anyways. But then it will also pass if osi-validation crashes due to some bug.

[ClemensLinnhoff]

I added a valid SensorView trace file to be tested in the CI. Now it passes.