Loading classes from multi-release jars does not work

[aguibert]

In Java 9, Multi-Release jars were added: https://openjdk.java.net/jeps/238

In short, this allows classes to be placed in different locations, such as:

jar root
  - A.class
  - B.class
  - C.class
  - D.class
  - META-INF
     - versions
        - 9
           - A.class
           - B.class
        - 10
           - A.class

This is handled automatically by URLClassLoader, and also by JarFile. However, liberty classloading does not make use of either of these constructs when it comes to classloading.

We will need to make additional changes in classloading and/or the artifact layer in order to support this.