Add a separate docker-init binary

This may be used for the .dockerinit case if the main binary is not
statically linked.

docker-init/docker-init.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"github.com/dotcloud/docker"
+)
+
+var (
+	GITCOMMIT string
+	VERSION   string
+)
+
+func main() {
+	// Running in init mode
+	docker.SysInit()
+	return
+}