Start VirtualBox VM before login (at reboot)

I want my VM to start at reboot and before login. I put this script in rc.local file to be executed before login and start my VirtualBox VM:

sudo -H -u  myuser /usr/bin/VBoxManage startvm "MyOS"

If I execute the file directly via terminal:

sudo /etc/rc.local

My VM will start correctly, but when reboot the OS nothing happens. What's wrong with that?

I tried to follow the instructions in this post: How to start Virtual box machines automatically when booting? but it's not working for me because I don't have any /etc/vbox folder on my Ubuntu 14.04 using VirtualBox 4.3.10_ubuntu r93012