Embedded Cassandra - support setting consistency level

Allow ECL developers to set consistency level for embedded cassandra statements.

https://docs.datastax.com/en/cassandra/3.0/cassandra/dml/dmlConfigConsistency.html

This will allow our cassandra projects to determine the appropriate consistency level used.

Also, the default consistency of the Cassandra c++ driver has changed over time.  At a minimum we need to be able to set the value so it doesn't change under the covers when we are not aware.