Update config to match upstream cassandra 2.1.17. (#2371)
Update config to match upstream cassandra 2.1.17. (#2371)

Mostly wanted it so Docker could configure broadcast_rpc_address from
the commented out option.
lolski/grakn,graknlabs/grakn,lolski/grakn,lolski/grakn,lolski/grakn,graknlabs/grakn,graknlabs/grakn,graknlabs/grakn