code: func (g *Cloud) GetAllZonesFromCloudProvider() (sets.String, error) {
  	ctx, cancel := cloud.ContextWithCallTimeout()
  	defer cancel()
  
  	zones := sets.NewString()
  	for _, zone := range g.managedZones {
  		instances, err := g.c.Instances().List(ctx, zone, filter.None)
  		if err != nil {
  			return sets.NewString(), err
  		}
  		if len(instances) > 0 {
  			zones.Insert(zone)
  		}
  	}
  	return zones, nil
  }
docs: // GetAllZonesFromCloudProvider returns all the zones in which nodes are running
  // Only use this in E2E tests to get zones, on real clusters this will
  // get all zones with compute instances in them even if not k8s instances!!!
  // ex. I have k8s nodes in us-central1-c and us-central1-b. I also have
  // a non-k8s compute in us-central1-a. This func will return a,b, and c.
  //
  // TODO: this should be removed from the cloud provider.