I havn't tried it out yet, but from somewhere, I found cirros: CirrOS is a Tiny OS that specializes in running on a cloud.
Some documentation show how to get it into an lxc container.
Should run as a really tiny kvm?
I found in a Debian install that CirrOS is an LXC template (with the install of the LXC package):
# ls -alt /usr/share/lxc/templates/lxc-cirros -rwxr-xr-x 1 root root 10374 Aug 25 18:20 /usr/share/lxc/templates/lxc-cirros