On VMWare fusion, running an Ubuntu Xenial VM, which has a copy of your OS X public SSH key -- the script to build the image will add it to the generated image -- grab the script at https://github.com/zyga/devtools/blob/master/ubuntu-image to create a new image:
./ubuntu-image.sh --developer-mode pc
qemu-img convert pc-devel.img -O vmdk snappy.vmdk