PyJobTransforms: Fix test failure on arm.
We don't define ATLASMKLLIBDIR_PRELOAD on arm. That results in no LD_PRELOAD being defined, which was causing test_trfEnv to fail. Tweak so that we don't fail in that case.
We don't define ATLASMKLLIBDIR_PRELOAD on arm. That results in no LD_PRELOAD being defined, which was causing test_trfEnv to fail. Tweak so that we don't fail in that case.