virt-aa-helper: allow access to /usr/share/ovmf/
We forbid access to /usr/share/, but (at least on Debian-based systems)
the Open Virtual Machine Firmware files needed for booting UEFI virtual
machines in QEMU live in /usr/share/ovmf/. Therefore, we need to add
that directory to the list of read only paths.
A similar patch was suggested by Jamie Strandboge <jamie@canonical.com>
on https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/
1483071.
(cherry picked from commit
2f01cfdf05448513d150ff1914d3444161c531b9)