Update go-cni to 40bcf8ec8acd7372be1d77031d585d5d8e561c90.

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

vendor/github.com/containerd/go-cni/cni.go

@@ -18,6 +18,7 @@ package cni
 
 import (
 	"fmt"
+	"strings"
 	"sync"
 
 	cnilibrary "github.com/containernetworking/cni/libcni"
@@ -127,6 +128,15 @@ func (c *libcni) Remove(id string, path string, opts ...NamespaceOpts) error {
 	}
 	for _, network := range c.networks {
 		if err := network.Remove(ns); err != nil {
+			// Based on CNI spec v0.7.0, empty network namespace is allowed to
+			// do best effort cleanup. However, it is not handled consistently
+			// right now:
+			// https://github.com/containernetworking/plugins/issues/210
+			// TODO(random-liu): Remove the error handling when the issue is
+			// fixed and the CNI spec v0.6.0 support is deprecated.
+			if path == "" && strings.Contains(err.Error(), "no such file or directory") {
+				continue
+			}
 			return err
 		}
 	}