apparmor: allow tunnelled migrations.

apparmor: allow tunnelled migrations.

The pathname for the pipe for tunnelled migration is unresolvable.  The
libvirt apparmor driver therefore refuses access, causing migration to
fail.  If we can't resolve the path, the worst that can happen is that
we should have given permission to the file but didn't.  Otherwise
(especially since this is a /proc/$$/fd/N file) the file is already open
and libvirt won't be refused access by apparmor anyway.

Also adjust virt-aa-helper to allow access to the
*.tunnelmigrate.dest.name files.

For more information, see https://launchpad.net/bugs/869553.

Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>