Fix compilation for Java 10

[chingor13]

• Update datanucleus plugin versions to build on Java 9/10.
• Update clirr-maven-plugin to 2.8 to work on Java 10.
• Removing Java 9 from the test matrix as we cannot resolve the issue and guava does not seem to work on Java 9 anyways.

[chingor13]

The Java 9 test was removed internally and should not run on future PRs.

[jeanbza]

Could you update the assembly versions, too? Also, this update will require syncing versions to the other two repos, assuming we don't split the release process soon.

[chingor13]

@jadekler The only versions that changed were the maven plugins which aren't included in the assembly - they only are used during the development and build process.

[jeanbza]

SGTM!