make upstream server names macro sensitive

etc-nginx-templates/default.conf.template

@@ -2,11 +2,11 @@
 # https://serverfault.com/questions/1011561/docker-based-reverse-proxy-with-nginx-for-multiple-domains
 
 upstream davrods {
-  server davrods:80;
+  server davrods_${MRDENV_MODE}:80;
 }
 
 upstream forms {
-  server forms:8080;
+  server forms_${MRDENV_MODE}:8080;
 }
 
 # Redirect all sites to https