Fix unit tests to load test/conf/cassandra.yaml (so to listen on a valid ip)

Many of the ci-cassandra jenkins runs fail on ip-10-0-5-5: Name or service not known. CASSANDRA-15622 addressed some of these but many still remain. Currently test C* nodes are either failing or listening on a public ip depending on which agent they end up.

The idea behind this ticket is to make ant force the private VPC ip in the cassandra yaml when building, this will force the nodes to listen on the correct ip.