Use k8s.gcr.io/pause:3.4.1 in pull-only tests

This reduces the need to pull random images from docker.io, and should
greatly reduce the tendancy to hit their hourly rate-limit during
integration test runs.

TestImagePullSomePlatforms uses k8s.gcr.io/pause:3.2 so that it does not
see the content pulled by TestImagePullAllPlatforms. This image is
multi-arch, but not multi-os.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

integration/client/lease_test.go

@@ -55,7 +55,7 @@ func TestLeaseResources(t *testing.T) {
 	defer ls.Delete(ctx, l, leases.SynchronousDelete)
 
 	// step 1: download image
-	imageName := "docker.io/library/busybox:1.25"
+	imageName := "k8s.gcr.io/pause:3.4.1"
 
 	image, err := client.Pull(ctx, imageName, WithPullUnpack, WithPullSnapshotter("native"))
 	if err != nil {