proxy: bring back pdc-backend, this one doesn't have anything to do with the pdc-backend hosts

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

roles/haproxy/templates/haproxy.cfg

@@ -215,6 +215,10 @@ backend openqa-backend
 
 frontend pdc-frontend
     bind 0.0.0.0:10045
+    default_backend pdc-backend
+
+backend pdc-backend
+    balance hdr(appserver)
 
 {% if env != "staging" %}
     # Set session persistence with a cookie.