nixos tests: move common configuration into separate file

This allows tests outside nixos to use acme setup.

nixos/tests/acme.nix

@@ -1,32 +1,5 @@
 let
-  commonConfig = { lib, nodes, ... }: {
+  commonConfig = ./common/letsencrypt/common.nix;
-    networking.nameservers = [
-      nodes.letsencrypt.config.networking.primaryIPAddress
-    ];
-
-    nixpkgs.overlays = lib.singleton (self: super: {
-      cacert = super.cacert.overrideDerivation (drv: {
-        installPhase = (drv.installPhase or "") + ''
-          cat "${nodes.letsencrypt.config.test-support.letsencrypt.caCert}" \
-            >> "$out/etc/ssl/certs/ca-bundle.crt"
-        '';
-      });
-
-      # Override certifi so that it accepts fake certificate for Let's Encrypt
-      # Need to override the attribute used by simp_le, which is python3Packages
-      python3Packages = (super.python3.override {
-        packageOverrides = lib.const (pysuper: {
-          certifi = pysuper.certifi.overridePythonAttrs (attrs: {
-            postPatch = (attrs.postPatch or "") + ''
-              cat "${self.cacert}/etc/ssl/certs/ca-bundle.crt" \
-                > certifi/cacert.pem
-            '';
-          });
-        });
-      }).pkgs;
-    });
-  };
-
 in import ./make-test.nix {
   name = "acme";
 

nixos/tests/common/letsencrypt/common.nix

@@ -0,0 +1,27 @@
+{ lib, nodes, ... }: {
+  networking.nameservers = [
+    nodes.letsencrypt.config.networking.primaryIPAddress
+  ];
+
+  nixpkgs.overlays = lib.singleton (self: super: {
+    cacert = super.cacert.overrideDerivation (drv: {
+      installPhase = (drv.installPhase or "") + ''
+        cat "${nodes.letsencrypt.config.test-support.letsencrypt.caCert}" \
+          >> "$out/etc/ssl/certs/ca-bundle.crt"
+      '';
+    });
+
+    # Override certifi so that it accepts fake certificate for Let's Encrypt
+    # Need to override the attribute used by simp_le, which is python3Packages
+    python3Packages = (super.python3.override {
+      packageOverrides = lib.const (pysuper: {
+        certifi = pysuper.certifi.overridePythonAttrs (attrs: {
+          postPatch = (attrs.postPatch or "") + ''
+            cat "${self.cacert}/etc/ssl/certs/ca-bundle.crt" \
+              > certifi/cacert.pem
+          '';
+        });
+      });
+    }).pkgs;
+  });
+}