webui-build: use /usr/share/java/js.jar instead of rhino.jar
    
    /usr/share/java/rhino.jar is a Fedora's symlink to /usr/share/java/js.jar
    
    Debian doesn't have it. Direct usage of upstream /usr/share/java/js.jar should
    work on both systems.
    
    Reviewed-By: Timo Aaltonen <tjaalton@ubuntu.com>