apparmor: Enable passt support

apparmor: Enable passt support

passt provides an AppArmor abstraction that covers all the
inner details of its operation, so we can simply import that
and add the libvirt-specific parts on top: namely, passt
needs to be able to create a socket and pid file, while
the libvirt daemon needs to be able to kill passt.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>