* SHAREDDISKSIZE can now be set to empty to avoid creation of shared
  disks.  However, the various node templates still contain the shared
  disk definitions so this causes an error.

  Need a way of working around this.  One possibility is to have a
  file containing a separate fragment for the shared disks and then
  process that along with other indirects.  However, this suggests
  that the handling of indirects needs to be generalised somehow.