Replace/upgrade findbugs to spotbugs (maven plugin, jenkins report, ...)

"SpotBugs is the spiritual successor of FindBugs, carrying on from the point where it left off with support of its community."

https://spotbugs.github.io/index.html

Maven plugin:
http://spotbugs.readthedocs.io/en/latest/maven.html

Let's make this change on all kie projects - Once the changes are know for the optaplanner, mbiarnes@redhat.com can help with bringing them to the other repo's too.