Fix review comments.

driver.go

@@ -678,12 +678,11 @@ func (d *Driver) SignalTask(taskID string, signal string) error {
 	// The given signal will be forwarded to the target taskID.
 	// Please checkout https://github.com/hashicorp/consul-template/blob/master/signals/signals_unix.go
 	// for a list of supported signals.
-	sig := os.Interrupt
-	if s, ok := signals.SignalLookup[signal]; ok {
-		sig = s
-	} else {
-		d.logger.Warn("unknown signal to send to task, using SIGINT instead", "signal", signal, "task_id", handle.taskConfig.ID)
+	sig, ok := signals.SignalLookup[signal]
+	if !ok {
+		return fmt.Errorf("Error in looking up signal: %s", signal)
 	}
+
 	return d.podmanClient.SignalContainer(handle.containerID, sig)
 }