* Return specialized error type
* Add a helper for extracting gRPC codes from errors
* Fix spacing in example
* Drop grpc codes
* Fix storing of decoded errors
* Allow returning list information and other data in 404s.
On read it'll output data and/or warnings on a 404 if they exist. On
list, the same behavior; the actual 'vault list' command doesn't change
behavior though in terms of output unless there are no actual keys (so
it doesn't just magically show other data).
This corrects some assumptions in response_util and wrapping.go; it also
corrects a few places in the latter where it could leak a (useless)
token in some error cases.
* Use same 404 logic in delete/put too
* Add the same secret parsing logic to the KV request functions
