Several refactorings, simplifications and small improvements:

• Remove jar_archive test. Unlike other tests, jar_archive is written in shell and we want to keep only Java tests. Besides that, functionality of jar_archive should be already covered by bytecode_version test that unpacks JAR files - it should fail in case .jar file is not a ZIP file.
• Merge test_scripts/common.sh into jp_validator.sh.
• Move jp_validator.sh out of test_scripts/ directory.
• Set environment variables directly in fmf file.
• Don't run podman in interactive mode.
• Use exec to run podman to save one fork.
• Fail on undefined environment variables.