Adding ssh public key to Ubuntu cloud image

ssh_ubuntu_cloud

# Instructions for working with QEMU image come from 
# https://www.kumari.net/index.php/system-adminstration/49-mounting-a-qemu-image 

1. Download image http://cloud-images.ubuntu.com/
2. Install qemu, nbd-client
3. Load the module
    sudo modprobe nbd max_part=8
4. Connect image  
    sudo qemu-nbd --connect=/dev/nbd0 Downloads/xenial-server-cloudimg-amd64-disk1.img
5. Mount image
    sudo mount /dev/nbd0p1 /mnt/cd
6. Add the content of ~/.ssh/id_rsa.pub to /mnt/cd/home/ubuntu/.ssh/authorized_keys
7. Unmount image
    sudo umount /mnt/cd
8. Disconnect the image
    sudo nbd-client -d /dev/nbd0