virt-aa-helper: handle more disk images

virt-aa-helper: handle more disk images

virt-aa-helper needs read access to the disk image to resolve symlinks
and add the proper rules to the profile. Its profile whitelists a few
common paths, but users can place their images anywhere.

This commit helps users allowing access to their images by adding their
own rules in apparmor.d/local/usr.lib.libvirt.virt-aa-helper.

This commit also adds rules to allow reading files named:
  - *.raw as this is a rather common disk image extension
  - /run/libvirt/**[vd]d[a-z] as these are used by virt-sandbox