move get functional test material(openj9 tests) to functional/build.xml

[sophia-guo]

In aqa-tests we have openjdk, system, perf, external, functional tests category. Each test category follows a similar structure and manage its own test material, i.e. with build.xml to gather test material ( git clone, curl, wget). This approach ensures simplicity, extensibility and low coupling.

Functional tests ( openj9 tests) are gathered differently getFunctionalTestMaterial() in get.sh by passing in extra parameters, which due to initially TKG was part of openj9. As TKG has its own repo it's time to move this process to functional/build.xml. This way when a new feature is enabled functional tests won't need to be considered differently, which might be missed, need extra tests and costs more. For example adoptium/TKG#651

[sophia-guo]

This could also make adding a functional/test.properties with openj9 repo and sha info possible #5151, which can avoid piling all infos to aqa-tests/testenv/testenv.properties and keep the file growing and choatic.