Filter out 0.0.0.0, if ever gotten from Cassandra in split calculation. ...

...Fixes #332.
How about
 
   ```scala
    final val NullAddress = InetAddress.getByName("0.0.0.0")```

```scala
    /* An incorrectly configured Cassandra node may send us 0.0.0.0 as the rpc_address.
     If this happens, we replace it with the local address (which must be always != 0.0.0.0) */
    def cassandraNode(rpcAddress: InetAddress, localAddress: InetAddress): CassandraNode =
      (rpcAddress, localAddress) match {
          case (NullAddress, NullAddress) =>  throw new IllegalArgumentException(
                  "Broadcast address and RPC address of a Cassandra node must not both be set to 0.0.0.0")
          case (rpc, local) => CassandraNode(rpc, local)
      }```