Don't write zeros to stdout

BuildKite occasionally shows;

> Warning: This log has exceeded the 1MB display limit. Below we are
> only showing the last 1MB of output.

This is because TestOOM_Isolated's dd writes 10MB of zeros to stdout.
It doesn't have to be.

Signed-off-by: Kazuyoshi Kato <[email protected]>

Author: kzys

runtime/service_integ_test.go

@@ -1849,9 +1849,11 @@ func TestOOM_Isolated(t *testing.T) {
 		containerd.WithSnapshotter(defaultSnapshotterName),
 		containerd.WithNewSnapshot("snapshot-"+vmID, image),
 		containerd.WithNewSpec(
-			oci.WithProcessArgs("/bin/dd", "if=/dev/zero", "ibs=10M"),
-			firecrackeroci.WithVMID(vmID),
+			// The container is having 2MB of memory.
 			oci.WithMemoryLimit(2*1024*1024),
+			// But the dd command allocates 10MB of data on memory, which will be OOM killed.
+			oci.WithProcessArgs("/bin/dd", "if=/dev/zero", "ibs=10M", "of=/dev/null"),
+			firecrackeroci.WithVMID(vmID),
 		),
 	)
 	require.NoError(t, err)