Hazelcast tests fail on networks where multicast is disabled

A new hazelcast instance will fail to join a cluster on networks where multicast is disabled. This can be solved via configuration on a production system, but the unit tests use the default configuration that from the hazelcast jar, which disables tcp and enables multicast. As a result one ends up with two clusters, on instance each instead of one cluster two instances.

Using a custom, minimal hazelcast.xml configuration solves the problem. See pull request.