Convert guest suffix from VMWare to QEMU:
user % qemu-img convert -c -p -O qcow2 vmname.vdmk vmname.qcow2
This works for the .ova too:
user % qemu-img convert -c -p -O qcow2 vmname.ova vmname.qcow2
And for the .vdi suffix as well:
user % qemu-img convert -c -p -O qcow2 vmname.vdi vmname.qcow2