virtcontainers: skip cgroup namespace check

Old kernels, like 3.x, does not support cgroup namespace. Skip the test that
checks this namespace if its path in /proc doesn't exist.

Depends-on: github.com/kata-containers/tests#1414

fixes kata-containers#228

Signed-off-by: Julio Montes <julio.montes@intel.com>

virtcontainers/pkg/nsenter/nsenter_test.go

@@ -84,6 +84,12 @@ func TestGetFileFromNSWrongNSPathFailure(t *testing.T) {
 func TestGetFileFromNSSuccessful(t *testing.T) {
 	for nsType := range CloneFlagsTable {
 		nsFilePath := fmt.Sprintf("/proc/self/ns/%s", string(nsType))
+		if _, err := os.Stat(nsFilePath); os.IsNotExist(err) {
+			// some namespaces, like cgroup, are too new for longterm distros with
+			// old kernels.
+			t.Logf("Namespace '%s' is not supported in this kernel. Update your kernel to a version >4.0", string(nsType))
+			continue
+		}
 		nsFile, err := getFileFromNS(nsFilePath)
 		assert.Nil(t, err, "Should have succeeded: %v", err)
 		assert.NotNil(t, nsFile, "The file handler should not be nil")