cluster_controller: shift log error on cluster update to info level

When scylla-operator is bringing cluster up on GKE it can raise "Failed to update cluster status, Operation cannot be fulfilled on"
This PR is to log this under INFO log level

Fixes  #217

pkg/controllers/cluster/cluster_controller.go

@@ -121,7 +121,11 @@ func (cc *ClusterReconciler) Reconcile(request ctrl.Request) (ctrl.Result, error
 	if !reflect.DeepEqual(c.Status, copy.Status) {
 		logger.Info(ctx, "Writing cluster status.")
 		if err := cc.Status().Update(ctx, copy); err != nil {
-			logger.Error(ctx, "Failed to update cluster status", "error", err)
+			if apierrors.IsConflict(err) {
+				logger.Info(ctx, "Failed to update cluster status", "error", err)
+			} else {
+				logger.Error(ctx, "Failed to update cluster status", "error", err)
+			}
 			return reconcile.Result{}, errors.WithStack(err)
 		}
 	}