Add plugin code

This adds basic plugins.
"main" types: veth, bridge, macvlan
"ipam" type: host-local

The code has been ported over from github.com/coreos/rkt project
and adapted to fit the CNI spec.

plugins/ipam/host-local/main.go

@@ -0,0 +1,85 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// 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.
+
+package main
+
+import (
+	"errors"
+
+	"github.com/appc/cni/plugins/ipam/host-local/backend/disk"
+
+	"github.com/appc/cni/pkg/plugin"
+	"github.com/appc/cni/pkg/skel"
+)
+
+func main() {
+	skel.PluginMain(cmdAdd, cmdDel)
+}
+
+func cmdAdd(args *skel.CmdArgs) error {
+	ipamConf, err := LoadIPAMConfig(args.StdinData)
+	if err != nil {
+		return err
+	}
+
+	store, err := disk.New(ipamConf.Name)
+	if err != nil {
+		return err
+	}
+	defer store.Close()
+
+	allocator, err := NewIPAllocator(ipamConf, store)
+	if err != nil {
+		return err
+	}
+
+	var ipConf *plugin.IPConfig
+
+	switch ipamConf.Type {
+	case "host-local":
+		ipConf, err = allocator.Get(args.Netns)
+	case "host-local-ptp":
+		ipConf, err = allocator.GetPtP(args.Netns)
+	default:
+		return errors.New("Unsupported IPAM plugin type")
+	}
+
+	if err != nil {
+		return err
+	}
+
+	return plugin.PrintResult(&plugin.Result{
+		IP4: ipConf,
+	})
+}
+
+func cmdDel(args *skel.CmdArgs) error {
+	ipamConf, err := LoadIPAMConfig(args.StdinData)
+	if err != nil {
+		return err
+	}
+
+	store, err := disk.New(ipamConf.Name)
+	if err != nil {
+		return err
+	}
+	defer store.Close()
+
+	allocator, err := NewIPAllocator(ipamConf, store)
+	if err != nil {
+		return err
+	}
+
+	return allocator.Release(args.Netns)
+}