Stop GCE instance rather than delete GCE instance

Since already defer function deletes GCE instance, this is for
preventing double deletion.

Author: 0405ysj

tools/baseimage/cmd/create_gce_x86_64_image/main.go

@@ -125,9 +125,9 @@ func createImageMain(project, zone string) error {
 	if err := gce.WaitForInstance(project, zone, insName); err != nil {
 		return fmt.Errorf("waiting for instance error: %v", err)
 	}
-	log.Printf("deleting instance %q...", insName)
-	if err := h.DeleteInstance(insName); err != nil {
-		return fmt.Errorf("error deleting instance: %v", err)
+	log.Printf("stopping instance %q...", insName)
+	if err := h.StopInstance(insName); err != nil {
+		return fmt.Errorf("error stopping instance: %v", err)
 	}
 	if err := h.CreateImage(insName, attachedDiskName, outImageName); err != nil {
 		return fmt.Errorf("failed to create image: %w", err)

tools/baseimage/pkg/gce/helper.go

@@ -122,6 +122,14 @@ func (h *GceHelper) CreateInstance(name string) (*compute.Instance, error) {
 	return payload, nil
 }
 
+func (h *GceHelper) StopInstance(name string) error {
+	op, err := h.Service.Instances.Stop(h.Project, h.Zone, name).Do()
+	if err != nil {
+		return err
+	}
+	return h.waitForOperation(op)
+}
+
 func (h *GceHelper) DeleteInstance(name string) error {
 	op, err := h.Service.Instances.Delete(h.Project, h.Zone, name).Do()
 	if err != nil {