Standard log package by default only prints out the second-scale
so the 3rd party log feeder mixes the order of the events, which makes
the debugging hard. This replaces it with capnslog and make them consistent
with all other etcd log formats.
when closed errors will be one of:
```
grpc.ErrorDesc(err) == context.Canceled.Error() ||
grpc.ErrorDesc(err) == context.DeadlineExceeded.Error() ||
grpc.ErrorDesc(err) == "transport is closing" ||
grpc.ErrorDesc(err) == "grpc: the client connection is closing"
```
Hash method returns either (nil, err) or (Hash, nil).
The current error checking is wrong. It only needs to check
the error is either nil or non-nil.
This causes panic in https://github.com/coreos/etcd/issues/4463
by allowing the case when resp is nil, but err is not nil.
