security: aa-helper: allow virt-aa-helper to read /dev/dri

Change fb01e1a4 "virt-aa-helper: generate rules for gl enabled
graphics devices" implemented the detection for gl enabled
devices in virt-aa-helper. But it will in certain cases e.g. if
no rendernode was explicitly specified need to read /dev/dri
which it currently isn't allowed.

Add a rule to the apparmor profile of virt-aa-helper itself to
be able to do that.
Acked-by: NJamie Strandboge <jamie@canonical.com>
Signed-off-by: NChristian Ehrhardt <christian.ehrhardt@canonical.com>

src/security/apparmor/usr.lib.libvirt.virt-aa-helper

@@ -19,6 +19,9 @@ profile virt-aa-helper /usr/{lib,lib64}/libvirt/virt-aa-helper {
 
   /etc/libnl-3/classid r,
 
+  # for gl enabled graphics
+  /dev/dri/{,*} r,
+
   # for hostdev
   /sys/devices/ r,
   /sys/devices/** r,