log critical error if key is not inserted due to policy parameters

If the policy parameters do not meet a given criteria the following message is logged:

Key lifetime unreasonably short with respect to TTL and MaxZoneTTL. Will not insert key!

and the zone will not be allocated keys and therefore will not be signed. I think that this should be logged as a (critical) error to make sure the user notices the problem! At the moment I believe it is just a warning.