Re-think integration vendoring

- remove docker/docker from  Traefik vendor (unused)
- use `ignore` for all Traefik vendor in integration glide.
- defined only integration specific version of the dependencies.

integration/vendor/github.com/opencontainers/runc/main_unix.go

@@ -2,4 +2,32 @@
 
 package main
 
-import _ "github.com/opencontainers/runc/libcontainer/nsenter"
+import (
+	"os"
+	"runtime"
+
+	"github.com/opencontainers/runc/libcontainer"
+	_ "github.com/opencontainers/runc/libcontainer/nsenter"
+	"github.com/urfave/cli"
+)
+
+func init() {
+	if len(os.Args) > 1 && os.Args[1] == "init" {
+		runtime.GOMAXPROCS(1)
+		runtime.LockOSThread()
+	}
+}
+
+var initCommand = cli.Command{
+	Name:  "init",
+	Usage: `initialize the namespaces and launch the process (do not call it outside of runc)`,
+	Action: func(context *cli.Context) error {
+		factory, _ := libcontainer.New("")
+		if err := factory.StartInitialization(); err != nil {
+			// as the error is sent back to the parent there is no need to log
+			// or write it to stderr because the parent process will handle this
+			os.Exit(1)
+		}
+		panic("libcontainer: container init failed to exec")
+	},
+}