Update findbugs plugin from 2.5.3 to 2.5.4
Simplify JaCoCo in pom - use defaults

Removes surefire section as part of simplification
Remove guava dependency, provided implicitly by jenkins core dependency

Guava updates can't be managed with "mvn versions:use-latest-releases"
because its version must exactly match the version included in jenkins
core.  Since it must exactly match the version included in Jenkins
core, there is little benefit to declaring the dependency explicitly
in this pom.