Use image lists instead of hardcoded images

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

integration/client/lease_test.go

@@ -23,6 +23,7 @@ import (
 	. "github.com/containerd/containerd"
 	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/images"
+	imagelist "github.com/containerd/containerd/integration/images"
 	"github.com/containerd/containerd/leases"
 	"github.com/opencontainers/image-spec/identity"
 )
@@ -55,7 +56,7 @@ func TestLeaseResources(t *testing.T) {
 	defer ls.Delete(ctx, l, leases.SynchronousDelete)
 
 	// step 1: download image
-	imageName := "k8s.gcr.io/pause:3.7"
+	imageName := imagelist.PauseImage
 
 	image, err := client.Pull(ctx, imageName, WithPullUnpack, WithPullSnapshotter(snapshotterName))
 	if err != nil {