Give more memory for the disk image builder

http://hydra.nixos.org/build/26480662

nixos/lib/make-disk-image.nix

@@ -39,6 +39,7 @@ pkgs.vmTools.runInLinuxVM (
       exportReferencesGraph =
         [ "closure" config.system.build.toplevel ];
       inherit postVM;
+      memSize = 1024;
     }
     ''
       ${if partitioned then ''

pkgs/build-support/vm/default.nix

@@ -302,13 +302,13 @@ rec {
      `run-vm' will be left behind in the temporary build directory
      that allows you to boot into the VM and debug it interactively. */
 
-  runInLinuxVM = drv: lib.overrideDerivation drv (attrs: {
+  runInLinuxVM = drv: lib.overrideDerivation drv ({ memSize ? 512, QEMU_OPTS ? "", args, builder, ... }: {
     requiredSystemFeatures = [ "kvm" ];
     builder = "${bash}/bin/sh";
     args = ["-e" (vmRunCommand qemuCommandLinux)];
-    origArgs = attrs.args;
-    origBuilder = attrs.builder;
-    QEMU_OPTS = "${attrs.QEMU_OPTS or ""} -m ${toString (attrs.memSize or 512)}";
+    origArgs = args;
+    origBuilder = builder;
+    QEMU_OPTS = "${QEMU_OPTS} -m ${toString memSize}";
   });