LPS-51439 Fix general purpose test target

Backport pull at https://github.com/brianchandotcom/liferay-portal-ee/pull/7721
Plugins is already doing this.

I found it really hard to fix the old broken logic. But base on what we have talked about, this general top level test target should just run any available tests under the current dir, which is what this pull doing and it makes things very simple.