Local apparmor include to tweak libvirt-qemu

This is already at its third iteration.
Discussions are on IRC in #ubuntu-hardened with jdstrand and jjohansen.

The TL;DR for now is:
- we don't want the profile reload from dh_apparmor as we are an abstraction
- dh_apparmor can't work with subdirs like abstractions/libvirt-qemu
- We only need a postinst snippet to ensure an empty include file is placed

If exist includes would make this even safer (no fail if the include doesn't exist), but what isn't in apparmor yet can't be used :-/

I have a working version of this in the upcoming lbvirt 4.6 ppa builds.
I submitted it to Debian where our other two local includes reside atm - to get their feedback and if they are willing to pick it as well.

=> https://salsa.debian.org/libvirt-team/libvirt/merge_requests/6

This bug was fixed in the package libvirt - 4.6.0-2ubuntu1

---------------
libvirt (4.6.0-2ubuntu1) cosmic; urgency=medium

  * Merged with Debian unstable (LP: #1786957).
    Among many other new features and fixes this includes fixes
    for (LP: #1754871), Remaining changes:
    - Disable libssh2 support (universe dependency)
    - Disable firewalld support (universe dependency)
    - Set qemu-group to kvm (for compat with older ubuntu)
    - Additional apport package-hook
    - Autostart default bridged network (As upstream does, but not Debian).
      In addition to just enabling it our solution provides:
      + do not autostart if subnet is already taken (e.g. in guests).
      + iterate some alternative subnets before giving up
    - d/p/ubuntu/Allow-libvirt-group-to-access-the-socket.patch: This is
      the group based access to libvirt functions as it was used in Ubuntu
      for quite long.
      + d/p/ubuntu/daemon-augeas-fix-expected.patch fix some related tests
        due to the group access change.
      + d/libvirt-daemon-system.postinst: add users in sudo to the libvirt
        group.
    - ubuntu/parallel-shutdown.patch: set parallel shutdown by default.
    - d/p/ubuntu/enable-kvm-spice.patch: compat with older Ubuntu qemu/kvm
      which provided a separate kvm-spice.
    - Xen related
      - d/p/ubuntu/ubuntu-libxl-qemu-path.patch: this change was split. The
        section that adapts the path of the emulator to the Debian/Ubuntu
        packaging is kept.
      - d/p/ubuntu/ubuntu-libxl-Fix-up-VRAM-to-minimum-requirements.patch: auto
        set VRAM to minimum requirements
      - d/p/ubuntu/xen-default-uri.patch: set default URI on xen hosts
      - Add libxl log directory
      - libvirt-uri.sh: Automatically switch default libvirt URI for users on
        Xen dom0 via user profile (was missing on changelogs before)
    - d/p/ubuntu/apibuild-skip-libvirt-common.h: drop libvirt-common.h from
      included_files to avoid build failures due to duplicate definitions.
    - Update README.Debian with Ubuntu changes
    - Convert libvirt0, libnss_libvirt and libvirt-dev to multi-arch.
    - Enable some additional features on ppc64el and s390x (for arch parity)
      + systemtap, zfs, numa and numad on s390x.
      + systemtap on ppc64el.
    - d/t/control, d/t/smoke-qemu-session: fixup smoke-qemu-session by making
      vmlinuz available and accessible (Debian bug 848314)
    - d/t/control, d/t/smoke-lxc: fix up lxc smoke test isolation
    - Add dnsmasq configuration to work with system wide dnsmasq (drop >18.04,
      no more UCA onto Xenial then which has global dnsmasq by default).
    - d/p/ubuntu/ubuntu_machine_type.patch: accept ubuntu types as pci440fx
    - Further upstreamed apparmor Delta, especially any new one
      Our former delta is split into logical pieces and is either Ubuntu only
      or is part of a continuous upstreaming effort.
      Listing related remaining changes in debian/patches/ubuntu-aa/:
      + 0001-apparmor-Allow-pygrub-to-run-on-Debian-Ubuntu.patch: apparmor:
        Allow pygrub to run on Debian/Ubuntu
      + 0003-apparmor-libvirt-qemu-Allow-read-access-to-overcommi.patch:
        ...