An optional script to run for installing the JRE or JDK during the NodePool setup phase. For example: 'apt-get
update && apt-get install openjdk-8-jre-headless -y'. If none provided, the default Ubuntu OpenJDK 8 JRE will be
installed. This script will only run if an existing java is not found. If java is pre-installed, then the existing
java is used for the Jenkins agent launch.