MXS-1262: Use monitor journals in all monitors

All monitors now persist the state of the server in a monitor journal
file.

Moved the removal of stale journals into the core and removed them from
the monitor journal interface.

server/modules/monitor/mysqlmon.h

@@ -78,7 +78,6 @@ typedef struct
                                    down before failover is initiated */
     bool allow_cluster_recovery; /**< Allow failed servers to rejoin the cluster */
     bool warn_failover; /**< Log a warning when failover happens */
-    bool load_journal; /**< Whether journal file should be loaded */
     bool allow_external_slaves; /**< Whether to allow usage of external slave servers */
     MXS_MONITOR* monitor;
 } MYSQL_MONITOR;