Replace ModulesUtil in test

[jbescos]

There are many failures in test when publicLookup is used.

I added a test class to replace existing classes in test-runtime:

• src/main/java/org/eclipse/yasson/internal/model/ModulesUtil.java
• src/main/java9/org/eclipse/yasson/internal/model/ModulesUtil.java

When tests are executed with maven-surefire-plugin the content of
'classes' is in a different module-path than 'test-classes'.

This causes the MethodHandles#publicLookup to fail. The reason is that
test classes to serialize/deserialize are coming from module 'test-classes'
and the module 'classes' has no access to it. The 'publicLookup' makes some
validations and because different modules, it fails.

This class is a workaround to bypass this issue, as it is happening in test only.

It should work if 'classes' and 'test-classes' are merged in one unique module. Probably you are questioning now, - why we don't merge both modules in one?. I actually tried it here:
https://github.com/jbescos/yasson/tree/publicLookupFix1

The problem is that we need to introduce a module-info in the test-classes and this brings a new set of problems. Currently I'm having the next issue and I don't know how to fix it:

[ERROR] WARNING: Unknown module: org.junit.platform.commons specified to --add-opens
[ERROR] WARNING: Unknown module: org.junit.platform.commons specified to --add-opens
[ERROR] java.lang.NoClassDefFoundError: org/junit/platform/commons/util/Preconditions