recent drcachesim tests using simple_app fail due to races on the output directory

I'm seeing a set of recently-added drcachesim tests failing when run in parallel:

The following tests FAILED:
	270 - code_api|tool.raw2trace.simple (Failed)
	326 - code_api,satisfy_w_xor_x|tool.drcacheoff.simple (Failed)
Errors while running CTest

They are using simple_app and they collide on the output directory name. We have other tests that do this as well but they're properly marked with dependencies. Unfortunately as we add more we have to mark even more as serial wrt each other. We may want to put a more-maintainable solution in place: a custom name for the output directory or something.