• make backing-image.qcow2 - downloads the backing image and extracts it
• qemu-img resize backing-image.qcow2 +10G - increases the size of the backing image
• make run-backing-image - runs the backing image for initial setup
• login with root:root
• lsblk - confirm the backing image size
• fdisk /dev/sda
• d 3 - delete the 3rd partition
• n 3 - create a new partition, use default options
• w - write changes
• reboot - reboot the machine, reload the partition table
• resize2fs /dev/sda3 - resize the partition
• Change /etc/ssh/sshd_config to: PermitRootLogin yes, PasswordAuthentication yes
• Setup ssh keys for zso, from host: ssh-copy-id -p 2222 zso@localhost
• Setup ssh keys for root, from host: ssh-copy-id -p 2222 root@localhost
• Copy your own ssh keys to the machine to use git and ssh: scp -P 2222 -r ~/.ssh zso@localhost:~
• apt-get update && apt-get install -y rsync
• close the virtual machine
• make current-image.qcow2 - creates the current image, backed by the backing image
• make run-current-image - runs the current image

You can add aliases to ssh config to simplify commands. In ~/.ssh/config:

Host zso-zso
  HostName localhost
  Port 2222
  User zso

Host root-zso
  HostName localhost
  Port 2222
  User root

Sources: https://sandilands.info/sgordon/increasing-kvm-virtual-machine-disk-using-lvm-ext4