[filesystem]: upgrade to v2021.12.07
    
    * revised nsswitch.conf rules for systemd
    * arch dropped the empty motd;
      so i added a pretty one for parabola instead
    * added VARIANT_ID to the os-release file
      as a reliable way to determine the init-system
    
    the rest of the changes were only to minimize the diff
    against the arch PKGBUILD