Some more changes for early support for JDK 18

Some more changes for early support for JDK 18

Adjust one test which fails with JDK 18 because of
remove SecurityManager
Adjust excludes for JaCoCo as it does not run on JDK 18 otherwise
Adjust some JPMS settings which are not available any more on JDK 18

Some other things do not work yet, e.g. spotbugs

Also print out if CIBuild is selected
Only run signing if actually publishing to avoid failures
if signing key is defined locally

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1895626 13f79535-47bb-0310-9956-ffa450edef68