Add support for OpenJDK 9
    
    JEP 220 (Modular Run-Time Images) completely changes the layout of the
    JDK/JRE files and directories. Specifically:
    
    "The bin directory will contain any command-line launchers defined by
    the modules linked into the image."
    
    And:
    
    "A JDK image will [...] no longer contain a jre subdirectory."
    
    This change updates the code to accept a JDK directory without a jre
    subdirectory.