cri: Make sure host sandbox files exist before adding them to mounts

As `setupSandboxFiles` was done in sandbox controller, it is difficult
here to know if the sandbox controller has done and where the host path
in. Make sure the host path exists before adding them to linux container
mounts, otherwise, the container would generate some unnecessary mounts.

Signed-off-by: Zhang Tianyang <burning9699@gmail.com>

internal/cri/server/container_create_test.go

@@ -733,32 +733,21 @@ func TestLinuxContainerMounts(t *testing.T) {
 			expectedMounts:  nil,
 		},
 		{
-			desc: "should skip hostname mount if the old sandbox doesn't have hostname file",
+			desc: "should skip sandbox mounts if the old sandbox doesn't have sandbox file",
 			statFn: func(path string) (os.FileInfo, error) {
-				assert.Equal(t, filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hostname"), path)
-				return nil, errors.New("random error")
+				sandboxRootDir := filepath.Join(testRootDir, sandboxesDir, testSandboxID)
+				sandboxStateDir := filepath.Join(testStateDir, sandboxesDir, testSandboxID)
+				switch path {
+				case filepath.Join(sandboxRootDir, "hostname"), filepath.Join(sandboxRootDir, "hosts"),
+					filepath.Join(sandboxRootDir, "resolv.conf"), filepath.Join(sandboxStateDir, "shm"):
+					return nil, errors.New("random error")
+				default:
+					t.Fatalf("expected sandbox files, got: %s", path)
+				}
+				return nil, nil
 			},
 			securityContext: &runtime.LinuxContainerSecurityContext{},
-			expectedMounts: []*runtime.Mount{
-				{
-					ContainerPath:  "/etc/hosts",
-					HostPath:       filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hosts"),
-					Readonly:       false,
-					SelinuxRelabel: true,
-				},
-				{
-					ContainerPath:  resolvConfPath,
-					HostPath:       filepath.Join(testRootDir, sandboxesDir, testSandboxID, "resolv.conf"),
-					Readonly:       false,
-					SelinuxRelabel: true,
-				},
-				{
-					ContainerPath:  "/dev/shm",
-					HostPath:       filepath.Join(testStateDir, sandboxesDir, testSandboxID, "shm"),
-					Readonly:       false,
-					SelinuxRelabel: true,
-				},
-			},
+			expectedMounts:  nil,
 		},
 	} {
 		test := test