nixos/tests/systemd-repart: make sizeDiff configurable

The +32M is not sufficient to create additional partitions.
Make it configurable.

nixos/tests/systemd-repart.nix

@@ -9,9 +9,16 @@ with pkgs.lib;
 
 let
   # A testScript fragment that prepares a disk with some empty, unpartitioned
-  # space. and uses it to boot the test with. Takes a single argument `machine`
+  # space. and uses it to boot the test with.
-  # from which the diskImage is extracted.
+  # Takes two arguments, `machine` from which the diskImage is extracted,
-  useDiskImage = machine: ''
+  # as well an optional `sizeDiff` (defaulting to +32M), describing how should
+  # be resized.
+  useDiskImage =
+    {
+      machine,
+      sizeDiff ? "+32M",
+    }:
+    ''
       import os
       import shutil
       import subprocess
@@ -27,7 +34,7 @@ let
         "-f",
         "raw",
         tmp_disk_image.name,
-      "+32M",
+        "${sizeDiff}",
       ])
 
       # Set NIX_DISK_IMAGE so that the qemu script finds the right disk image.
@@ -98,7 +105,7 @@ in
     testScript =
       { nodes, ... }:
       ''
-        ${useDiskImage nodes.machine}
+        ${useDiskImage { inherit (nodes) machine; }}
 
         machine.start()
         machine.wait_for_unit("multi-user.target")
@@ -128,7 +135,7 @@ in
     testScript =
       { nodes, ... }:
       ''
-        ${useDiskImage nodes.machine}
+        ${useDiskImage { inherit (nodes) machine; }}
 
         machine.start()
         machine.wait_for_unit("multi-user.target")
@@ -196,7 +203,7 @@ in
     testScript =
       { nodes, ... }:
       ''
-        ${useDiskImage nodes.machine}
+        ${useDiskImage { inherit (nodes) machine; }}
 
         machine.start()
         machine.wait_for_unit("multi-user.target")