Add containerd main binary code

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

.gitignore

@@ -7,3 +7,4 @@ main
 /hack/benchmark
 /output
 /example/example
+/cli/containerd/containerd

cli/containerd/main.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"syscall"
+
+	"google.golang.org/grpc"
+
+	"github.com/Sirupsen/logrus"
+	"github.com/docker/containerd"
+	"github.com/urfave/cli"
+)
+
+func main() {
+	app := cli.NewApp()
+	app.Name = "containerd"
+	app.Version = containerd.Version
+	app.Usage = `
+                    __        _                     __
+  _________  ____  / /_____ _(_)___  ___  _________/ /
+ / ___/ __ \/ __ \/ __/ __ ` + "`" + `/ / __ \/ _ \/ ___/ __  / 
+/ /__/ /_/ / / / / /_/ /_/ / / / / /  __/ /  / /_/ /  
+\___/\____/_/ /_/\__/\__,_/_/_/ /_/\___/_/   \__,_/   
+                                                      
+high performance container runtime
+`
+	app.Flags = []cli.Flag{
+		cli.BoolFlag{
+			Name:  "debug",
+			Usage: "enable debug output in logs",
+		},
+		cli.StringFlag{
+			Name:  "socket, s",
+			Usage: "socket path for containerd's GRPC server",
+			Value: "/run/containerd/containerd.sock",
+		},
+	}
+	app.Before = func(context *cli.Context) error {
+		if context.GlobalBool("debug") {
+			logrus.SetLevel(logrus.DebugLevel)
+		}
+		return nil
+	}
+	app.Action = func(context *cli.Context) error {
+		signals := make(chan os.Signal, 2048)
+		signal.Notify(signals, syscall.SIGTERM, syscall.SIGINT)
+
+		path := context.GlobalString("socket")
+		if path == "" {
+			return fmt.Errorf("--socket path cannot be empty")
+		}
+		if err := os.MkdirAll(filepath.Dir(path), 0660); err != nil {
+			return err
+		}
+		if err := syscall.Unlink(path); err != nil && !os.IsNotExist(err) {
+			return err
+		}
+		l, err := net.Listen("unix", path)
+		if err != nil {
+			return err
+		}
+
+		server := grpc.NewServer()
+		go serve(server, l)
+
+		for s := range signals {
+			switch s {
+			default:
+				logrus.WithField("signal", s).Info("containerd: stopping GRPC server")
+				server.Stop()
+				return nil
+			}
+		}
+		return nil
+	}
+	if err := app.Run(os.Args); err != nil {
+		fmt.Fprintf(os.Stderr, "containerd: %s\n", err)
+		os.Exit(1)
+	}
+}
+
+func serve(server *grpc.Server, l net.Listener) {
+	defer l.Close()
+	if err := server.Serve(l); err != nil {
+		l.Close()
+		logrus.WithError(err).Fatal("containerd: GRPC server failure")
+	}
+}