cluster/nix: symlink /sbin/lvm

This is needed by the new Rook OSD daemons.

Change-Id: I16eb24332db40a8209e7eb9747a81fa852e5cad9
diff --git a/cluster/nix/modules/base.nix b/cluster/nix/modules/base.nix
index 034d1cd..29f2072 100644
--- a/cluster/nix/modules/base.nix
+++ b/cluster/nix/modules/base.nix
@@ -54,6 +54,15 @@
   # Use Chrony instead of systemd-timesyncd
   services.chrony.enable = true;
 
+  # Symlink lvm into /sbin/lvm on activation. This is needed by Rook OSD
+  # instances running on Kubernetes.
+  # See: https://github.com/rook/rook/commit/f3c4975e353e3ce3599c958ec6d2cae8ee8f6f61
+  system.activationScripts.sbinlvm =
+    ''
+      mkdir -m 0755 -p /sbin
+      ln -sfn ${pkgs.lvm2.bin}/bin/lvm /sbin/lvm
+    '';
+
   # Enable the OpenSSH daemon.
   services.openssh.enable = true;
   users.users.root.openssh.authorizedKeys.keys = [