Spotbugs default $JAVA_HOME not set

Summary

Spotbugs uses dynamic environment setup for customizing the java version and load path. In the default cases however, JAVA_HOME is not set since it only gets defined when SetupSystemJava is triggered.

Even in default cases, JAVA_HOME should be set. We should trigger update_java_home during startup.

Steps to reproduce

1. Start docker container
2. Check JAVA_HOME, see undefined

Example Project

❯ docker run -it --rm registry.gitlab.com/gitlab-org/security-products/analyzers/spotbugs:2 bash
bash-5.0# echo $JAVA_HOME

What is the current bug behavior?

$JAVA_HOME is undefined even with default java version (8)

What is the expected correct behavior?

$JAVA_HOME should point to default java version (8)