MXS-1744 Use gtid querying instead of MASTER_GTID_WAIT when waiting for catchup

MASTER_GTID_WAIT uses gtid_slave_pos when comparing to the target gtid. This creates
problems with multi-domain gtids. It's simpler to just query the server for its
gtids repeatedly. Also, the method is now in MariaDBServer.

server/modules/monitor/mariadbmon/gtid.hh

@@ -147,13 +147,11 @@ public:
                                  substraction_mode_t domain_substraction_mode);
 
     /**
-     * Generate a MASTER_GTID_WAIT()-query to this gtid.
+     * Return an individual gtid with the given domain.
      *
-     * @param timeout Maximum wait time in seconds
-     * @return The query
+     * @param domain Which domain to search for
+     * @return The gtid within the list. If domain is not found, an invalid gtid is returned.
      */
-    std::string generate_master_gtid_wait_cmd(double timeout) const;
-
     Gtid get_gtid(uint32_t domain) const;
 
 private: