MXS-839: Detect multi-master topologies with mysqlmon

The mysqlmon now supports proper detection of multi-master topologies by
building a directed graph out of the monitored server. If cycles are found from
this graph, they are assigned a master group ID. All servers with a positive
master group ID will receive the Master status unless they have `@@read_only`
enabled.

This new functionality can be enabled with the 'multimaster' boolean
parameter.

server/core/config.c

@@ -184,6 +184,7 @@ static char *monitor_params[] =
     "available_when_donor",
     "disable_master_role_setting",
     "use_priority",
+    "multimaster",
     NULL
 };