Make unit tests of CassandraIO use embedded server

The UT currently use a mock of the cassandra server. It would be good to do the tests using embeded Cassandra instance to be as close as possible from a real Cassandra server in the UT. Why not the one from cassandra-unit (https://mvnrepository.com/artifact/org.cassandraunit/cassandra-unit/3.3.0.2) ?