Broadcast/discovery-group resources have ambiguous requirement specs

Currently, the broadcast/discovery-group resources have messy requirement specs, as the capabilities that they require are dependent whether or not the jgroups-cluster attribute is defined.

I suggest splitting these resources into 2:

/subsystem=messaging-activemq/server=*/jgroups-broadcast-group=*

/subsystem=messaging-activemq/server=*/jgroups-discovery-group=*

which requires clustering capabilities

and

/subsystem=messaging-activemq/server=*/socket-broadcast-group=*

/subsystem=messaging-activemq/server=*/socket-discovery-group=*

which requires a socket-binding capability.

This results in clearer requirement specs - which helps simplify the introspection of this subsystem for provisioning purposes.