nixos/elasticsearch: fix postStart to allow non-localhost listenAddress

Before this fix, if the listenAddress is set to something else than 127.0.0.1,
the service fails to detect that Elasticsearch has properly started and stop.

nixos/modules/services/search/elasticsearch.nix

@@ -204,7 +204,7 @@ in
       postStart = ''
         # Make sure elasticsearch is up and running before dependents
         # are started
-        while ! ${pkgs.curl}/bin/curl -sS -f http://localhost:${toString cfg.port} 2>/dev/null; do
+        while ! ${pkgs.curl}/bin/curl -sS -f http://${cfg.listenAddress}:${toString cfg.port} 2>/dev/null; do
           sleep 1
         done
       '';