Change printer management logic so that saved managed printer list is not
used when querying and updating printers.

Added new options:
--delete-unmanaged to delete printers that are not managed. This is used
  now for shared laptops that should not keep changes made by the user.

--no-dns-query to disable DNS queries when using --delete-unmanaged during
  boottime

--require-dns-records to instruct the script to not delete printer information
  if DNS-SD records were not found
client: Do not delete all printer information on shared laptops during boot,
        but only the unmanaged printers.