Tests: When deleting the stage "@test", use robust common code.
Tests: When deleting the stage "@test", use robust common code.

* This is to eliminate all direct usages of "shutil.rmtree" and seems
  like a good idea.

* Also added a TODO about integrating the Windows only trick of calling
  an external process into that function.

kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka