MXS-2011 Use alternative servers

If the replication fails using the current config, we retry
immediately using another config, without waiting anything at
all.

Only when we have unsuccessfully tried with all servers, will
we wait a while before starting again.

server/modules/routing/binlogrouter/blr.hh

@@ -821,7 +821,8 @@ struct ROUTER_INSTANCE: public MXS_ROUTER
     enum binlog_storage_type   storage_type;/*< Enables hierachical binlog file storage */
     char              *set_slave_hostname;  /*< Send custom Hostname to Master */
     ROUTER_INSTANCE  *next;
-    std::vector<ChangeMasterConfig> configs;              /*< Current config. */
+    std::vector<ChangeMasterConfig> configs;/*< Available configs. */
+    int               current_config;       /*< The config currently being used. */
 };
 
 /** Master Semi-Sync capability */