lnrpc+rpc+lnd: add new Stop command for gracefully shutting down lnd

This commit adds simple non-blocking stop command to lncli, with an
appropriate proto update and implementation within the rpcserver.  When
invoked the interrupt handler routine in signal.go with begin the graceful
shutdown of lnd.

cmd/lncli/commands.go

@@ -1550,3 +1550,23 @@ func listChainTxns(ctx *cli.Context) error {
 	printRespJSON(resp)
 	return nil
 }
+
+var stopCommand = cli.Command{
+	Name:        "stop",
+	Usage:       "Stop and shutdown the daemon.",
+	Description: "Gracefully stop all daemon subsystems before stopping the daemon itself. This is equivalent to stopping it using CTRL-C.",
+	Action:      stopDaemon,
+}
+
+func stopDaemon(ctx *cli.Context) error {
+	ctxb := context.Background()
+	client, cleanUp := getClient(ctx)
+	defer cleanUp()
+
+	_, err := client.StopDaemon(ctxb, &lnrpc.StopRequest{})
+	if err != nil {
+		return err
+	}
+
+	return nil
+}

cmd/lncli/main.go

@@ -79,6 +79,7 @@ func main() {
 		debugLevelCommand,
 		decodePayReqComamnd,
 		listChainTxnsCommand,
+		stopCommand,
 	}
 
 	if err := app.Run(os.Args); err != nil {