Simplify initialization of replication

The users are now created on both the slaves as well as the master. This
allows static binlog coordinates to be used on the slaves and the
replication initialization boils down to a set of SQL queries.

maxscale-system-test/mariadb_nodes.h

@@ -411,6 +411,12 @@ public:
     virtual int prepare_server(int i);
     int prepare_servers();
 
+    /**
+     * Static functions
+     */
+
+    /** Whether to require GTID based replication, defaults to false */
+    static void require_gtid(bool value);
 
 private: