Goals

1. Make sure parent poms provide maven plugins supporting Java 9, 10, 11...
   1. validate through release lifecycle (how we missed the issue with site-plugin last time)
   2. define a migration path such that newer Java versions can be used but class files stay compatible with Java 8 until all dependencies have been migrated.
2. Find where this triggers compile issues (as in mvn test-compile), without tests
3. Pave the way for modern test execution
   1. on JDK9+ (more effort, mockito 2 upgrade, etc.); file tickets
   2. using JUnit5, running both new/old tests with both jupiter/vintage engines

Execution

• 6.2 will remain on java 8
• Prepare branches on 6.2 with necessary changes for Java 11 (e.g. upgrade to Mockito 2.x) but keep the base version at Java 8.
• When we do get 6.3 branches then those would build on 11 initially, with 17 coming in a 2nd step
• Ensure modules still produce class file versions that are compatible with Java 8: keep javaVersion at 8 but build with Java 11 on Jenkins. Start bumping javaVersion to 11 starting with leaf modules once all relevant modules build on Java 11.