legacy: legacy directory pre-creation

* Ensures legacy directories are pre-created
  upon legacy extension setup_app() call.
  (closes #1789)

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>
No problem in using the new format, just... why? Is it improving speed? Or is just for readability? what about the old %{path}s etc.?