Use uvtool to create a machine:

sudo apt install uvtool

Download cloud images with

uvt-simplestreams-libvirt --verbose sync release=xenial arch=amd64

Images and meta-data are located under /var/lib/uvtool/libvirt.

uvt-kvm create --cpu 2 --memory 2048 testvm release=xenial arch=amd64

testvm is the name of the VM. You can use that for various other commands:

uvt-kvm wait --insecure testvm
uvt-kvm ip testvm
uvt-kvm ssh --insecure testvm

The --insecure is needed for ssh to disable host key verification.