lxc: set NIX_PATH

lib/lxc/default.nix

@@ -5,6 +5,7 @@ let
   profilesDir = "/nix/var/nix/profiles/lxc";
   gcRoots = "/nix/var/nix/gcroots/lxc";
   containers = config.lxc.containers;
+  nixPath = config.nix.nixPath;
 in {
   options = with types; {
     lxc.containers = mkOption {
@@ -31,6 +32,9 @@ in {
 
             serviceConfig.Type = "oneshot";
             serviceConfig.RemainAfterExit = true;
+            serviceConfig.Environment = [
+              ''NIX_PATH=${builtins.concatStringsSep ":" nixPath}''
+            ];
 
             script = ''
               mkdir -p ${profilesDir}/${name}