improve Reproducible Builds

rebuilding Zookeeper 3.9.0 shows that it's only partially reproducible: https://github.com/jvm-repo-rebuild/reproducible-central/blob/master/content/org/apache/zookeeper/README.md

analysis the root cause, there are 3 issues:
1. a few old plugins to upgrade (easy)
2. code generated that contains build timestamp: replacing with git commit timestamp would make the build reproducible (or even removing this, but removing is a bigger change as it impacts API)
3. non-reproducible order of a properties files probably generated