go vet fixes

`go vet` had a few complaints:

```
client.go:36: struct field tag `json: "consistency"` not compatible with reflect.StructTag.Get
client.go:419: struct field tag `json: "config"` not compatible with reflect.StructTag.Get
client.go:420: struct field tag `json: "cluster"` not compatible with reflect.StructTag.Get
watch.go:55: unreachable code
watch.go:83: unreachable code
```

Do you care about go 1.0 still?