virt-aa-helper: locking loader/nvram for qemu 2.10

Testing qemu-2.10-rc3 shows issues like:
  qemu-system-aarch64: -drive file=/home/ubuntu/vm-start-stop/vms/
  7936-0_CODE.fd,if=pflash,format=raw,unit=1: Failed to unlock byte 100

There is an apparmor deny due to qemu now locking those files:
 apparmor="DENIED" operation="file_lock" [...]
 name="/home/ubuntu/vm-start-stop/vms/7936-0_CODE.fd"
 name="/var/lib/uvtool/libvirt/images/kvmguest-artful-normal.qcow"
 [...] comm="qemu-system-aarch64" requested_mask="k" denied_mask="k"

The profile needs to allow locking for loader and nvram files via
the locking (k) rule.
Signed-off-by: NChristian Ehrhardt <christian.ehrhardt@canonical.com>

src/security/virt-aa-helper.c

@@ -1029,11 +1029,11 @@ get_files(vahControl * ctl)
             goto cleanup;
 
     if (ctl->def->os.loader && ctl->def->os.loader->path)
-        if (vah_add_file(&buf, ctl->def->os.loader->path, "r") != 0)
+        if (vah_add_file(&buf, ctl->def->os.loader->path, "rk") != 0)
             goto cleanup;
 
     if (ctl->def->os.loader && ctl->def->os.loader->nvram)
-        if (vah_add_file(&buf, ctl->def->os.loader->nvram, "rw") != 0)
+        if (vah_add_file(&buf, ctl->def->os.loader->nvram, "rwk") != 0)
             goto cleanup;
 
     for (i = 0; i < ctl->def->ngraphics; i++) {