Since moving the JCP to separate module / jar, the JREFinder dialog cannot work, because it relies on launching "java -classpath <path>/deploy.jar com.sun.deploy.panel.java.JreLocator"
The main class name is right, but the classpath arg isn't. Now that JRELocation is no longer in deploy.jar we need:
'java -classpath "<path>/controlpanel.jar;<path>/deploy.jar" com.sun.deploy.panel.java.JreLocator'