LAN nginx proxies to the container name fluksio-api, which the test stack's backend does not carry

docker/nginx-api-proxy.conf

@@ -11,7 +11,10 @@ location ~ ^/(api|hooks) {
     # Docker's embedded DNS, re-resolved: nginx otherwise pins the backend's
     # address at startup and 502s for good once that container is recreated.
     resolver 127.0.0.11 valid=10s ipv6=off;
-    set $backend_upstream http://backend:8000;
+    # The container name, which only the dev API carries. The test stack's
+    # backend answers to the service name `backend` on the shared proxy
+    # network too.
+    set $backend_upstream http://fluksio-api:8000;
     proxy_pass $backend_upstream$request_uri;
 
     proxy_http_version 1.1;