Use mountpoint as image fs identifier.

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

pkg/server/service_test.go

@@ -33,7 +33,7 @@ const (
 	// TODO(random-liu): Change this to image name after we have complete image
 	// management unit test framework.
 	testSandboxImage = "sha256:c75bebcdd211f41b3a460c7bf82970ed6c75acaab9cd4c9a4e125b03ca113798"
-	testImageFSUUID  = "test-image-fs-uuid"
+	testImageFSPath  = "/test/image/fs/path"
 )
 
 // newTestCRIContainerdService creates a fake criContainerdService for test.
@@ -45,7 +45,7 @@ func newTestCRIContainerdService() *criContainerdService {
 				SandboxImage: testSandboxImage,
 			},
 		},
-		imageFSUUID:        testImageFSUUID,
+		imageFSPath:        testImageFSPath,
 		os:                 ostesting.NewFakeOS(),
 		sandboxStore:       sandboxstore.NewStore(),
 		imageStore:         imagestore.NewStore(),