erp5.balancer: Make haproxy add no-cache header when setting cookie.

Reason for not using postonly instead is that anonymous persistence may be
good in some erp5 use cases (ex: shopping cart), and also authentication
cookie may outlive haproxy cookie and may lead to no persistence afterward.

stack/erp5/buildout.cfg

@@ -350,7 +350,7 @@ md5sum = dedfe759c3421e0186703fe1257bae8f
 [template-haproxy-cfg]
 < = download-base
 filename = haproxy.cfg.in
-md5sum = 1dcb02721a606360271ca19d2f4d135b
+md5sum = d27fe9218cb737d8a76ba5df4740f947
 
 [template-logrotate-base]
 < = template-jinja2-base

stack/erp5/haproxy.cfg.in

@@ -11,7 +11,7 @@ defaults
   retries 1
   option redispatch
   maxconn 2000
-  cookie SERVERID insert
+  cookie SERVERID insert nocache
   balance roundrobin
   stats uri /haproxy
   stats realm Global\ statistics