nixos-modules/microvm/ssh-deploy: work around missing networking.hostName

NixOS/nixos-search#785 (comment)

Author: astro

nixos-modules/microvm/asserts.nix

@@ -1,7 +1,7 @@
 { config, lib, ... }:
 let
-
   inherit (config.networking) hostName;
+
 in
 lib.mkIf config.microvm.guest.enable {
   assertions =

nixos-modules/microvm/ssh-deploy.nix

@@ -1,7 +1,7 @@
 { config, lib, pkgs, ... }:
 
 let
-  inherit (config.networking) hostName;
+  hostName = config.networking.hostName or "$HOSTNAME";
   inherit (config.system.build) toplevel;
   inherit (config.microvm) declaredRunner;
   inherit (config) nix;