The jigsaw/m2 forest is currently accumulating the changes for the move to a modular image. The modular image will replace the current JRE/JDK layout. The replacement for j2sdk-image will not not have a top-level "jre" directory. The replacement for both j2sdk-image and j2re-image will not contain rt.jar, tools.jar and other JAR files, instead the classes and resources will be stored in a new container format.
com/sun/tools/extcheck/TestExtcheckArgs.java needs to be updated to remove its dependency on jconsole.jar that ships with the JDK. There will be no jconsole.jar or other JAR files in the modular image.