Configurable maximum number of ports to use for cluster

Makes the number of ports to use by the cluster configurable (it was hardcoded as 100).

In most cases this is not an issue, since there will not be more than 100 hazelcast
instances running on a single machine. But in those rare cases where this is needed
(e.g. for testing) this property can be set. If not set, it will default to 100, so
there will not be any change if not configured explicitly.