In elastic#81400 we changed `superuser` to no longer have _every_ privilege.
Consequently, we also removed the special case code that existed that
would ignore all other roles for any user that had superuser role.

However, we added some special handling so that failing to resolve those
other roles would not block superuser access - when a user has superuser
role, any failures in role resolution will be effectively ignored, and
the user will be given the superuser role only.

However, this failure handling did not account for the loading of
application privileges. If application privileges needed to be loaded,
but failed, this could prevent resolution of the superuser role.

This change extends the failure handling to encompass the full
resolution of roles, and fallback to superuser only, whenever other
roles or application privileges are unavailable

Relates: elastic#85312