MXS-2546 Separate slave connection settings to its own class

The settings are different from the other fields in that they should not change
on their own. Most manipulation functions only require the settings.

Also takes into use a class for host and port data.

server/modules/monitor/mariadbmon/cluster_discovery.cc

@@ -189,7 +189,8 @@ void MariaDBMonitor::build_replication_graph()
                 bool is_external = false;
                 if (use_hostnames)
                 {
-                    found_master = get_server(slave_conn.master_host, slave_conn.master_port);
+                    found_master = get_server(slave_conn.settings.master_endpoint.host(),
+                                              slave_conn.settings.master_endpoint.port());
                     if (!found_master)
                     {
                         // Must be an external server.