virt-aa-helper: fix libusb access to udev usb descriptions

In bf3a4140 "virt-aa-helper: fix libusb access to udev usb data" the
libusb access to properly detect the device/bus ids was fixed.

The path /run/udev/data/+usb* contains a subset of that information we
already allow to be read and are currently not needed for the function
qemu needs libusb for. But on the init of libusb all those files are
still read so a lot of apparmor denials can be seen when using usb host
devices, like:
  apparmor="DENIED" operation="open" name="/run/udev/data/+usb:2-1.2:1.0"
  comm="qemu-system-x86" requested_mask="r" denied_mask="r"

Today we could silence the warnings with a deny rule without breaking
current use cases. But since the data in there is only a subset of those
it can read already it is no additional information exposure. And on the
other hand a future udev/libusb/qemu combination might need it so allow
the access in the default apparmor profile.
Signed-off-by: NChristian Ehrhardt <christian.ehrhardt@canonical.com>

examples/apparmor/libvirt-qemu

@@ -32,6 +32,7 @@
   # libusb needs udev data about usb devices (~equal to content of lsusb -v)
   /run/udev/data/c16[6,7]* r,
   /run/udev/data/c18[0,8,9]* r,
+  /run/udev/data/+usb* r,
 
   # WARNING: this gives the guest direct access to host hardware and specific
   # portions of shared memory. This is required for sound using ALSA with kvm,