Allow DiscoveryLegacyConfiguration to add known configured ServiceURLs to the discovery mechanism

DiscoveryLegacyConfiguration is an ExternalDiscoveryProvider which was intended to take node and cluster information from the the legacy jboss-ejb-client.properties file and create ServiceURLs which can add to the ServiceURL knowledge base that a client has about target nodes.

This class was never fully implemented and needs to be completed.

One important use of this class could be in allowing a client to discover (via configured legacy clustering information) cluster ServiceURLs which would not otherwise be available before a first interaction with the cluster. This would allow SLSB invocations to proceed without depending on some other mechanism (such as EJBRemotingDiscoveryProvider) to provide such information for it.