Parse JUnit skipped tests as warnings

[TWiStErRob]

Thoughts?

(to skip a test either @Ignore it or throw AssumptionViolatedException() e.g. via org.junit.Assume.*)

Background: I just migrated away from my custom parser to the built-in one, and noticed this as one big difference.

reference PR (might need to manually expand JUnitParser.kt)

Happy to pull this, but wanted to check first if you agree.

[tomasbjerre]

I think it sounds good and a PR is welcome!