apparmor: Allow access to /sys/devices/system/node/*/cpumap for libnuma

apparmor: Allow access to /sys/devices/system/node/*/cpumap for libnuma

A QEMU change (10218ae6d006f76410804cc4dc690085b3d008b5) introduced
some libnuma calls that require read access to
/sys/devices/system/node/*/cpumap, which currently is forbidden by the
standard apparmor profile.

This commit allows read-only access to the file specified above.

Closes: https://gitlab.com/libvirt/libvirt/-/issues/515
Signed-off-by: Sergio Durigan Junior <sergio.durigan@canonical.com>
Reviewed-by: Jim Fehlig <jfehlig@suse.com>