MXS-1845 Assign server roles

Assign server roles (master, slave, relay master, slave of external master)
for a graph with possibly multiple paths to a slave server.

server/modules/monitor/mariadbmon/mariadbserver.hh

@@ -261,6 +261,13 @@ public:
      */
     bool is_relay_server() const;
 
+    /**
+     * Getter for m_read_only.
+     *
+     * @return True if server is in read_only mode
+     */
+    bool is_read_only() const;
+
     /**
      * Returns the server name.
      *