restclient must be able to deal with multiple types of servers. Alter
the behavior of restclient.Result#Raw() to not process the body on
error, but instead to return the generic error (which still matches the
error checking cases in api/error like IsBadRequest). If the caller uses
.Error(), .Into(), or .Get(), try decoding the body as a Status.
For older servers, continue to default apiVersion "v1" when calling
restclient.Result#Error(). This was only for 1.1 servers and the
extensions group, which we have since fixed.
This removes a double decode of very large objects (like LIST).
Also allow a new AcceptContentTypes field to allow the client to ask for
a fallback serialization when getting responses from the server. This
allows a new client to ask for protobuf and JSON, falling back to JSON
when necessary.
The changes to request.go allow error responses from non-JSON servers to
be properly decoded.
The codec factory should support two distinct interfaces - negotiating
for a serializer with a client, vs reading or writing data to a storage
form (etcd, disk, etc). Make the EncodeForVersion and DecodeToVersion
methods only take Encoder and Decoder, and slight refactoring elsewhere.
In the storage factory, use a content type to control what serializer to
pick, and use the universal deserializer. This ensures that storage can
read JSON (which might be from older objects) while only writing
protobuf. Add exceptions for those resources that may not be able to
write to protobuf (specifically third party resources, but potentially
others in the future).
