osbase/bringup/test: fix flake in bringup test

Change-Id: I17f51ea922be95e2d81b972b406bee13de3d202c
Reviewed-on: https://review.monogon.dev/c/monogon/+/3813
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/osbase/bringup/test/main_succeeded.go b/osbase/bringup/test/main_succeeded.go
index 930455c..b86d314 100644
--- a/osbase/bringup/test/main_succeeded.go
+++ b/osbase/bringup/test/main_succeeded.go
@@ -3,6 +3,7 @@
 import (
 	"context"
 	"fmt"
+	"time"
 
 	"golang.org/x/sys/unix"
 
@@ -12,6 +13,7 @@
 func main() {
 	bringup.Runnable(func(ctx context.Context) error {
 		fmt.Println("_BRINGUP_LAUNCH_SUCCESS_")
+		time.Sleep(5 * time.Second)
 		unix.Reboot(unix.LINUX_REBOOT_CMD_POWER_OFF)
 		return nil
 	}).Run()