Redundancy of public `exists_locally` vs `check_exists_locally`

[TomNicholas]

I feel like we don't need two public methods that do basically the same thing. Instead we might just have one read-only property exists_locally which internally calls a private method _check_exists_locally.

[dafyddstephenson]

Is the suggestion here just to rename check_exists_locally to indicate it's non-public?

There is a broader issue here in that exists_locally can't be set at init by a call to check_exists_locally, as the latter takes a path as an argument to determine where to look, and until InputDataset.get(tgt_path) has been called, it's unclear where to check for local existence.

When called from within Case.check_is_setup, it is clear what path to provide to InputDataset.check_exists_locally based on Case.caseroot .