client/v3: Add backoff before retry when watch stream returns unavailable
client/v3: Add backoff before retry when watch stream returns unavailable

The client retries connection without backoff when the server is gone
after the watch stream is established. This results in high CPU usage
in the client process. This change introduces backoff when the stream is
failed and unavailable.

Signed-off-by: Hisanobu Tomari <b361050090904d43e17f430ded5cc996f660ba25@gmail.com>

ajityagaty/etcd,ajityagaty/etcd,etcd-io/etcd,ajityagaty/etcd,etcd-io/etcd,etcd-io/etcd