Reject authentication data change when there are warnings

Reject authentication data change when there are warnings

AuthManager uses a status which is OK but not good for authentication
data which is discouraged but still accepted for authentication.
Users should not be allowed to change credentials into such invalid state.
This change brings the web logic and the AuthPlugin fallback in sync with
the API which already used the stricter check.

Change-Id: I4ff54fcc901f6fe11f15ed60fc1a3d8753de9f6c