Improve reconnection logic, allow jitters. (#3502)

Attempt a reconnect also if disk not found.

This is needed since any network operation error
is converted to disk not found but we also need
to make sure if disk is really not available. 

Additionally we also need to retry more than
once because the server might be in startup
sequence which would render other servers to
wrongly think that the server is offline.

cmd/retry.go

@@ -90,7 +90,7 @@ func newRetryTimer(unit time.Duration, cap time.Duration, jitter float64, doneCh
 
 	go func() {
 		defer close(attemptCh)
-		var nextBackoff int
+		nextBackoff := 1
 		for {
 			select {
 			// Attempts starts.