nixos: fix linux containers (systemd-nspawn, lxc, lxc-libvirt)

- Make dhcp work, use dhcpcd without udev in container
- Make login shell work, patch getty to not wait for /dev/tty0
- Make ssh work, sshd/pam do not start session

nixos/modules/services/networking/ssh/sshd.nix

@@ -285,7 +285,7 @@ in
     networking.firewall.allowedTCPPorts = cfg.ports;
 
     security.pam.services.sshd =
-      { startSession = true;
+      { startSession = !config.boot.isContainer;
         showMotd = true;
         unixAuth = cfg.passwordAuthentication;
       };