cri: Fix TestUpdateOCILinuxResource for host w/o swap controller

Tested on Ubuntu 20.04 w/o swap controller:
```
$ stat -fc %T /sys/fs/cgroup/
tmpfs
$ la -la /sys/fs/cgroup/memory/memory.memsw.limit_in_bytes
ls: cannot access '/sys/fs/cgroup/memory/memory.memsw.limit_in_bytes': No such file or directory
$  go test -v ./pkg/cri/sbserver/ -run TestUpdateOCILinuxResource
=== RUN   TestUpdateOCILinuxResource
=== RUN   TestUpdateOCILinuxResource/should_be_able_to_patch_the_unified_map
=== RUN   TestUpdateOCILinuxResource/should_be_able_to_update_each_resource
=== RUN   TestUpdateOCILinuxResource/should_skip_empty_fields
=== RUN   TestUpdateOCILinuxResource/should_be_able_to_fill_empty_fields
--- PASS: TestUpdateOCILinuxResource (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_be_able_to_patch_the_unified_map (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_be_able_to_update_each_resource (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_skip_empty_fields (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_be_able_to_fill_empty_fields (0.00s)
PASS
ok      github.com/containerd/containerd/pkg/cri/sbserver       (cached)
$ go test -v ./pkg/cri/server/ -run TestUpdateOCILinuxResource
=== RUN   TestUpdateOCILinuxResource
=== RUN   TestUpdateOCILinuxResource/should_be_able_to_update_each_resource
=== RUN   TestUpdateOCILinuxResource/should_skip_empty_fields
=== RUN   TestUpdateOCILinuxResource/should_be_able_to_fill_empty_fields
=== RUN   TestUpdateOCILinuxResource/should_be_able_to_patch_the_unified_map
--- PASS: TestUpdateOCILinuxResource (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_be_able_to_update_each_resource (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_skip_empty_fields (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_be_able_to_fill_empty_fields (0.00s)
    --- PASS: TestUpdateOCILinuxResource/should_be_able_to_patch_the_unified_map (0.00s)
PASS
ok      github.com/containerd/containerd/pkg/cri/server (cached)
```

Signed-off-by: Qasim Sarfraz <qasimsarfraz@microsoft.com>

pkg/cri/opts/spec_linux.go

@@ -411,7 +411,8 @@ var (
 	swapControllerAvailabilityOnce sync.Once
 )
 
-func swapControllerAvailable() bool {
+// SwapControllerAvailable returns true if the swap controller is available
+func SwapControllerAvailable() bool {
 	swapControllerAvailabilityOnce.Do(func() {
 		const warn = "Failed to detect the availability of the swap controller, assuming not available"
 		p := "/sys/fs/cgroup/memory/memory.memsw.limit_in_bytes"
@@ -481,7 +482,7 @@ func WithResources(resources *runtime.LinuxContainerResources, tolerateMissingHu
 		if limit != 0 {
 			s.Linux.Resources.Memory.Limit = &limit
 			// swap/memory limit should be equal to prevent container from swapping by default
-			if swapLimit == 0 && swapControllerAvailable() {
+			if swapLimit == 0 && SwapControllerAvailable() {
 				s.Linux.Resources.Memory.Swap = &limit
 			}
 		}

pkg/cri/sbserver/container_update_resources_linux_test.go

@@ -26,11 +26,18 @@ import (
 	runtime "k8s.io/cri-api/pkg/apis/runtime/v1"
 
 	criconfig "github.com/containerd/containerd/pkg/cri/config"
+	criopts "github.com/containerd/containerd/pkg/cri/opts"
 )
 
 func TestUpdateOCILinuxResource(t *testing.T) {
 	oomscoreadj := new(int)
 	*oomscoreadj = -500
+	expectedSwap := func(swap int64) *int64 {
+		if criopts.SwapControllerAvailable() {
+			return &swap
+		}
+		return nil
+	}
 	for desc, test := range map[string]struct {
 		spec      *runtimespec.Spec
 		request   *runtime.UpdateContainerResourcesRequest
@@ -72,7 +79,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),
@@ -118,7 +125,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),
@@ -159,7 +166,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),
@@ -208,7 +215,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),

pkg/cri/server/container_update_resources_linux_test.go

@@ -26,11 +26,18 @@ import (
 	runtime "k8s.io/cri-api/pkg/apis/runtime/v1"
 
 	criconfig "github.com/containerd/containerd/pkg/cri/config"
+	criopts "github.com/containerd/containerd/pkg/cri/opts"
 )
 
 func TestUpdateOCILinuxResource(t *testing.T) {
 	oomscoreadj := new(int)
 	*oomscoreadj = -500
+	expectedSwap := func(swap int64) *int64 {
+		if criopts.SwapControllerAvailable() {
+			return &swap
+		}
+		return nil
+	}
 	for desc, test := range map[string]struct {
 		spec      *runtimespec.Spec
 		request   *runtime.UpdateContainerResourcesRequest
@@ -72,7 +79,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),
@@ -118,7 +125,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),
@@ -159,7 +166,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),
@@ -208,7 +215,7 @@ func TestUpdateOCILinuxResource(t *testing.T) {
 					Resources: &runtimespec.LinuxResources{
 						Memory: &runtimespec.LinuxMemory{
 							Limit: proto.Int64(54321),
-							Swap:  proto.Int64(54321),
+							Swap:  expectedSwap(54321),
 						},
 						CPU: &runtimespec.LinuxCPU{
 							Shares: proto.Uint64(4444),