Vendor github.com/containernetworking/cni libcni and pkg file needed for CHECK

Update plugins/tests to deal with changes made to this vendor'ed code

plugins/meta/flannel/flannel.go

@@ -20,6 +20,7 @@ package main
 
 import (
 	"bufio"
+	"context"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -160,7 +161,7 @@ func delegateAdd(cid, dataDir string, netconf map[string]interface{}) error {
 		return err
 	}
 
-	result, err := invoke.DelegateAdd(netconf["type"].(string), netconfBytes, nil)
+	result, err := invoke.DelegateAdd(context.TODO(), netconf["type"].(string), netconfBytes, nil)
 	if err != nil {
 		return err
 	}

plugins/meta/flannel/flannel_linux.go

@@ -19,6 +19,7 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"github.com/containernetworking/cni/pkg/invoke"
@@ -82,5 +83,5 @@ func doCmdDel(args *skel.CmdArgs, n *NetConf) error {
 		return fmt.Errorf("failed to parse netconf: %v", err)
 	}
 
-	return invoke.DelegateDel(nc.Type, netconfBytes, nil)
+	return invoke.DelegateDel(context.TODO(), nc.Type, netconfBytes, nil)
 }