Convert VirtualBox .ova to .qcow2
extract the disk image
tar -xvf junos-vsrx-12.1X47-D20.7-domestic.ova
convert VMDK to QCOW2 format
qemu-img convert -O qcow2 junos-vsrx-12.1X47-D20.7-domestic-disk1.vmdk junos-vsrx-12.1X47-D20.7-domestic.qcow2
extract the disk image
tar -xvf junos-vsrx-12.1X47-D20.7-domestic.ova
convert VMDK to QCOW2 format
qemu-img convert -O qcow2 junos-vsrx-12.1X47-D20.7-domestic-disk1.vmdk junos-vsrx-12.1X47-D20.7-domestic.qcow2