Moved packages to pi_common

Deployments/pi_common.nix

@@ -0,0 +1,13 @@
+# Configuration common to all my servers
+
+{ config, pkgs, lib, ... }:
+
+{
+
+  environment = {       # Set the system-wide environment
+    systemPackages = with pkgs; [
+      lsusb             # Tools for working with USB devices, such as lsusb
+    ];
+  };
+
+}

Networks/pi3B_rack.nix

@@ -11,6 +11,7 @@
         <nixpkgs/nixos/modules/installer/scan/not-detected.nix>
         ../Hardware/raspberry_pi_3_model_B.nix
         ../Deployments/host_common.nix
+        ../Deployments/pi_common.nix
         ../Hosts/pi-tri.nix
         ../Hosts/pi-ceithir/nix
       ];
@@ -34,10 +35,6 @@
       ];
     };
 
-    environment.systemPackages = with pkgs; [
-      lsusb   # Tools for working with USB devices, such as lsusb
-    ];
-
     system.stateVersion = "19.09"; # Did you read the comment?
     system.autoUpgrade.enable = true;
     system.autoUpgrade.channel = https://nixos.org/channels/nixos-19.09;