Automatic merge from submit-queue

Allow etcd to store protobuf objects

Split storage serialization from client negotiation, and allow API server to take flag controlling serialization.

TODO:

* [x] API server still doesn't start - range allocation object doesn't seem to round trip correctly to etcd
* [ ] Verify that third party resources are ignoring protobuf (add a test)
* [ ] Add integration tests that verify storage is correctly protobuf
* [ ] Add a global default for which storage format to prefer?