This is what the spec recommends and it has been the case before
workflow-restarts, when `apps.webauthn.fido2` was imported exactly once
per lifetime.
With workflow-restarts, `fido2` is being imported repeatedly and the
keys regenerated. This does not seem to be a problem per the spec -- a
FIDO workflow will retain the same keys, and non-FIDO workflows can be
seen as unplugs/replugs as far as the FIDO functionality is concerned.
However, regenerating the keys is slow, which is a problem for the
hardware-based unit tests. We can avoid the slowness by returning to the
spec-mandated behavior and generating once per power-up.
