(wip) Setup btrfs impermanence

hosts/nixos-testbed/configuration.nix

@@ -6,6 +6,7 @@
   ];
 
   sydnix = {
+    filesystemType = "btrfs";
     impermanence = {
       enable = false;
       directories = [
@@ -13,10 +14,12 @@
         # This means all users/groups without specified uids/gids will have them
         # reassigned on reboot."
         "/var/lib/nixos"
+        # We don't want to have different ssh keys on reboot, because ssh keys
+        # are expected to consistently identify machines... I think.  I mostly
+        # just think it's annoying to edit ~/.ssh/known_hosts all the time.
         "/etc/ssh"
       ];
-      rollbackTo = "blank";
-      dataset = "rpool/local/home";
+      device = "placeholderrrr";
       archiveLimit = 3;
     };
     users.users = [