Use kernel specific for virtualization

Use  linux-image-kvm kernel which is designed for KVM virtualization.

For example, in Ubuntu, you should execute following commands: 

apt install linux-image-kvm
apt purge linux-image-generic
Clean up before publishing a template 
# removes logs
journalctl --vacuum-size=1
# removes user history
history -c
(as root) rm /root/.bash_history