change Location API for clarity on when config is inherited or not

change Location API for clarity on when config is inherited or not
(fixes bug recently introduced somehow where privateKeyFile was not respected for BYON)

api slightly clunkier but much safer. if we move to a model where config is never inherited and always copied (which i'd be in favour of) then we can revert the api -- however semantics there will have changed (always inherited) so this deprecation step is a good one in preparation for that improvement.