apparmor: fix qemu_bridge_helper for named profile

Since a3ab6d42 "apparmor: convert libvirtd profile to a named profile"
the detection of the subelement for qemu_bridge_helper is wrong.

In combination with the older 123cc3e1 "apparmor: allow
/usr/lib/qemu/qemu-bridge-helper" it now detects qemu-bridge-helper no
more with its path, but instead as a proper subelement of the named profile
like: label=libvirtd//qemu_bridge_helper

In the same fashion the reverse rule in the qemu_bridge_helper
sub-profile still uses the path and not the named profile label.

Triggering denies like:
apparmor="DENIED" operation="file_inherit"
  profile="libvirtd//qemu_bridge_helper" pid=5629 comm="qemu-bridge-hel"
  family="unix" sock_type="stream" protocol=0 requested_mask="send receive"
  denied_mask="send receive" addr=none peer_addr=none peer="libvirtd"

This patch fixes the unix socket rules for the communication between
libvirtd and qemu-bridge-helper to match that.

Fixes: a3ab6d42
Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1655111Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>
Signed-off-by: NChristian Ehrhardt <christian.ehrhardt@canonical.com>

src/security/apparmor/usr.sbin.libvirtd

@@ -61,8 +61,8 @@ profile libvirtd /usr/sbin/libvirtd flags=(attach_disconnected) {
   signal (send) set=("kill", "term") peer=unconfined,
 
   # For communication/control to qemu-bridge-helper
-  unix (send, receive) type=stream addr=none peer=(label=/usr/sbin/libvirtd//qemu_bridge_helper),
-  signal (send) set=("term") peer=/usr/sbin/libvirtd//qemu_bridge_helper,
+  unix (send, receive) type=stream addr=none peer=(label=libvirtd//qemu_bridge_helper),
+  signal (send) set=("term") peer=libvirtd//qemu_bridge_helper,
 
   # allow connect with openGraphicsFD, direction reversed in newer versions
   unix (send, receive) type=stream addr=none peer=(label=libvirt-[0-9a-f]*-[0-9a-f]*-[0-9a-f]*-[0-9a-f]*-[0-9a-f]*),
@@ -120,7 +120,7 @@ profile libvirtd /usr/sbin/libvirtd flags=(attach_disconnected) {
    network inet stream,
 
    # For communication/control from libvirtd
-   unix (send, receive) type=stream addr=none peer=(label=/usr/sbin/libvirtd),
+   unix (send, receive) type=stream addr=none peer=(label=libvirtd),
    signal (receive) set=("term") peer=/usr/sbin/libvirtd,
    signal (receive) set=("term") peer=libvirtd,