General improvements to debconf configuration handling

General improvements to debconf configuration handling

* General improvements to debconf configuration handling.
  - Do not abort the config script if we have no default realm and
    dnsdomainname fails.  (LP: #274886, #318132)
  - Do not abort postinst if we can't resolve any host name for the
    cell.  Just continue in that case, omitting any configuration for
    the local cell.  (LP: #322054)
  - Correctly set the default for AFS_CRYPT from the existing config.
  - The cache size is high, not critical, since we have a default.
  - Don't create the client ThisCell if no local cell was specified.
  - Improve the leading comment in afs.conf.client.  Users can edit it,
    but any changes other than the setting values will be lost.
  - Remove the openafs-fileserver/bosconfig_moved template, which would
    only be shown on upgrades from pre-1.2.0 versions.
  - Standardize coding style and always quote strings.