[manual] Serve static files from the same location across prod deploys

This only affects DEPLOYED installations.

This does not take care of removing old versions of static files from
that directory.  The problem is that staticfiles is clever and
doesn't copy files that are already there, so we can't depend on
mtime for detecting which files we no longer need.  Hopefully that
won't be too much of a problem for now.

(imported from commit 4341460dd5bc6544086fd445014ebdac58192910)

servers/puppet/modules/humbug/files/nginx/humbug-include/app

@@ -9,7 +9,7 @@ error_page 502 503 504 /static/html/5xx.html;
 
 # Serve static files directly
 location /static/ {
-    alias /home/humbug/humbug-deployments/current/prod-static/serve/;
+    alias /home/humbug/prod-static/;
     error_page 404 /static/html/404.html;
 }