Different approach, always create npmuser

even if the user id is zero, and then we'll always use it

docker/rootfs/etc/nginx/nginx.conf

@@ -1,6 +1,7 @@
 # run nginx in foreground
 daemon off;
 pid /run/nginx/nginx.pid;
+user npmuser;
 
 # Set number of worker processes automatically based on number of CPU cores.
 worker_processes auto;