virt-aa-helper: resolve yet to be created paths

virt-aa-helper: resolve yet to be created paths

In certain cases a xml contains paths that do not yet exist, but
are valid as qemu will create them later on - for example
vhostuser mode=server sockets.

In any such cases so far the check to virFileExists failed and due to
that the paths stayed non-resolved in regard to symlinks.

But for apparmor those non-resolved rules are non functional as they
are evaluated after resolving any symlinks.

Therefore for non-existent files and partially non-existent paths
resolve as much as possible to get valid rules.

Example:
   <interface type='vhostuser'>
       <model type='virtio'/>
       <source type='unix' path='/var/run/symlinknet' mode='server'/>
   </interface>

Got rendered as:
  "/var/run/symlinknet" rw,

But correct with "/var/run" being a symlink to "/run" is:
  "/run/symlinknet" rw,

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Acked-by: Michal Privoznik <mprivozn@redhat.com>