Redo how we test mod_cluster transformers to improve test coverage

The typical way subsystems test transformers is with a single transform xml file which contains all transformable attributes and resources to the oldest version (EAP 6.4 at the moment). However, as subsystems evolve certain attributes are not transformable but are missing from subsequent test coverage. For instance, attribute not present in EAP 6.4, but available since 7.0: the tests for EAP 7.1 could still test the transformation to EAP 7.0 but this is typically missed in the subsystems test coverage.

The solution is to use a specific file for each EAP controller version we are transforming to.