Create specific SSF rack configuration

Allow xeon machines to optionally inherit SSF configuration such as the
NFS mount point and the network configuration.

Reviewed-by: Aleix Boné <abonerib@bsc.es>

m/common/ssf/fs.nix

@@ -0,0 +1,8 @@
+{
+  # Mount the home via NFS
+  fileSystems."/home" = {
+    device = "10.0.40.30:/home";
+    fsType = "nfs";
+    options = [ "nfsvers=3" "rsize=1024" "wsize=1024" "cto" "nofail" ];
+  };
+}