Use containerd WithUserID.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/server/sandbox_run_test.go

@@ -128,16 +128,14 @@ func TestGenerateSandboxContainerSpec(t *testing.T) {
 			},
 			expectErr: true,
 		},
-		"should set user correctly": {
+		"should set supplemental groups correctly": {
 			configChange: func(c *runtime.PodSandboxConfig) {
 				c.Linux.SecurityContext = &runtime.LinuxSandboxSecurityContext{
-					RunAsUser:          &runtime.Int64Value{Value: 255},
 					SupplementalGroups: []int64{1111, 2222},
 				}
 			},
 			specCheck: func(t *testing.T, spec *runtimespec.Spec) {
 				require.NotNil(t, spec.Process)
-				assert.EqualValues(t, spec.Process.User.UID, 255)
 				assert.Contains(t, spec.Process.User.AdditionalGids, uint32(1111))
 				assert.Contains(t, spec.Process.User.AdditionalGids, uint32(2222))
 			},