Move git clone openj9 repo in functional level

[llxia]

Currently, we do git clone openj9 repo (in get.sh) regardless of what type of tests we run. We did this because TKG was in openj9 repo and we need to get TKG for running tests. With TKG separated out the of openj9 repo, we should move git clone openj9 repo in build.xml under functional dir https://github.com/adoptium/aqa-tests/tree/master/functional. That is, only git clone openj9 repo if we run functional tests. This would simplify the process and reduce testing overhead.