This tutorial has been inspired by flyingpenguin.
I wanted to try to install a Kali on OpenStack but there was no images available. I do not know if it is only on this OpenStack installation but it only accepted the upload of qcow2 formated images. I did not find an image with this file format and found a way to do it.
Install the necessary dependencies.
sudo aptitude install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils virt-goodies p7zip-full
Get the image
wget http://images.kali.org/Kali-Linux-2.0.0-vbox-amd64.7z
Unarchive the image
7z x Kali-Linux-2.0.0-vbox-amd64.7z
Extract the vmdk from the ova
tar xvf Kali-Linux-2.0.0-vbox-amd64.ova
Create the qcow2 file
qemu-img convert -O qcow2 Kali-Linux-2.0.0-vbox-amd64-disk1.vmdk Kali-Linux-2.0.0-vbox-amd64.qcow2