[TEST] Extend unicast ports generation to support more concurrent clusters

The current `UnicastZen` only supports up to 10 different clusters per jvm, after which it generates ports that overlap between different jvms.

Make it possible to run multiple tests with unicast configuration, by assigning ports based on their test scope.
Every jvm still gets its own port range based on the jvm id, but we now make sure that the different jvms ranges never overlap. The global cluster gets a reserved port range, while SUITE and TEST scopes are treated equally, just assuming that they never run concurrently on the same jvm, thus ports can be safely reused.
this is used for the unicast discovery - can we this back to the class? (or reuse the old variable :) )