`get_paths_for` only looks for parent dirs for `easyconfigs` (in this case). The subdirs are specific to the software being built, and we keep that separate.

Could be refactor to make `get_paths_for` works differently, but I don't see a good reason for it?

Right now, `get_paths_for` is generic, i.e. it can be used to look for others stuff than just `easyconfigs`, for which letter subdirs would make no sense.