Windows Support

Patch for https://github.com/containernetworking/plugins/pull/85

+ Windows cni plugins are added
   (*) win-bridge (hostgw)
   (*) win-overlay (vxlan)
+ Windows netconf unit test
+ Fix appveyor config to run the test
+ Build release support for windows plugins

Address comments

From:
    - https://github.com/containernetworking/plugins/pull/85
    - 0049c64e3f

plugins/meta/flannel/flannel_linux.go

@@ -0,0 +1,86 @@
+// Copyright 2018 CNI authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This is a "meta-plugin". It reads in its own netconf, combines it with
+// the data from flannel generated subnet file and then invokes a plugin
+// like bridge or ipvlan to do the real work.
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/containernetworking/cni/pkg/invoke"
+	"github.com/containernetworking/cni/pkg/skel"
+	"github.com/containernetworking/cni/pkg/types"
+	"os"
+)
+
+func doCmdAdd(args *skel.CmdArgs, n *NetConf, fenv *subnetEnv) error {
+	n.Delegate["name"] = n.Name
+
+	if !hasKey(n.Delegate, "type") {
+		n.Delegate["type"] = "bridge"
+	}
+
+	if !hasKey(n.Delegate, "ipMasq") {
+		// if flannel is not doing ipmasq, we should
+		ipmasq := !*fenv.ipmasq
+		n.Delegate["ipMasq"] = ipmasq
+	}
+
+	if !hasKey(n.Delegate, "mtu") {
+		mtu := fenv.mtu
+		n.Delegate["mtu"] = mtu
+	}
+
+	if n.Delegate["type"].(string) == "bridge" {
+		if !hasKey(n.Delegate, "isGateway") {
+			n.Delegate["isGateway"] = true
+		}
+	}
+	if n.CNIVersion != "" {
+		n.Delegate["cniVersion"] = n.CNIVersion
+	}
+
+	n.Delegate["ipam"] = map[string]interface{}{
+		"type":   "host-local",
+		"subnet": fenv.sn.String(),
+		"routes": []types.Route{
+			{
+				Dst: *fenv.nw,
+			},
+		},
+	}
+
+	return delegateAdd(args.ContainerID, n.DataDir, n.Delegate)
+}
+
+func doCmdDel(args *skel.CmdArgs, n *NetConf) error {
+	netconfBytes, err := consumeScratchNetConf(args.ContainerID, n.DataDir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			// Per spec should ignore error if resources are missing / already removed
+			return nil
+		}
+		return err
+	}
+
+	nc := &types.NetConf{}
+	if err = json.Unmarshal(netconfBytes, nc); err != nil {
+		return fmt.Errorf("failed to parse netconf: %v", err)
+	}
+
+	return invoke.DelegateDel(nc.Type, netconfBytes, nil)
+}