discovery-group and connector attributes are mutually exclusive

when creating bridges/cluster connections/JMS connection factories and other similar messaging resources, the user can specify either a discovery group (to discover the HornetQ nodes dynamically) or a set of connectors (for a static model).

The messaging subsystem model does not enforce this. The discovery-group-name and connectors attributes are mutually exclusive and the presence of 1 (and only 1) of them is mandatory.