For jtreg tests, ignore package clauses that do not match directory structure, or that lead outside of test root.

[lahodaj]

The source path for jtreg tests is inferred (among other things) from the package clause. But, this may lead to computation of weird source roots that are outside of the test directory. This PR is striving to not follow the package clause if:

• the directory structure does not match the package clause
• the inferred source root would be outside of the specific test directory

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