READ only database coherency fix

The document mentionned that we could use
 the rest of nodes as read only nodes, however the
 configuration suggest to use only one.

Change-Id: I418cd0e0bd00b093356ecca3d949e5ad44ba260e

doc/source/journey/configure/database.rst

@@ -112,11 +112,11 @@ If you choose to run haproxy for this, you can use something like the following
    
    listen db_slave
      bind 0.0.0.0:3308
-     balance first
+     balance roundrobin
      option mysql-check
-     server server-1 server-1.with.the.fqdn check inter 5s downinter 15s fastinter 2s resolvers cluster backup id 3
-     server server-2 server-2.with.the.fqdn check inter 5s downinter 15s fastinter 2s resolvers cluster id 1
-     server server-3 server-3.with.the.fqdn check inter 5s downinter 15s fastinter 2s resolvers cluster backup id 2
+     server server-1 server-1.with.the.fqdn check inter 5s downinter 15s fastinter 2s resolvers cluster id 3 backup
+     server server-2 server-2.with.the.fqdn check inter 5s downinter 15s fastinter 2s resolvers cluster id 1 weight 10
+     server server-3 server-3.with.the.fqdn check inter 5s downinter 15s fastinter 2s resolvers cluster id 2 weight 10
 
 By using two blocks, we can separate the ``read`` only SQL requests (listening on port 3308 here) from ``read/write``
 requests (listening on port 3306 here) and lower down a little bit the load on the first (master) mysql backend.