etcd server
To improve debuggability of etcd v3. Added a grpc interceptor to log
info on incoming requests to etcd server. The log output includes
remote client info, request content (with value field redacted), request
handling latency, response size, etc. Uses zap logger if available,
otherwise uses capnslog.
Also did some clean up on the chaining of grpc interceptors on server
side.
Jingyi Hu