Add result for set_keyspace response

In https://github.com/datastax/java-driver/pull/1267/commits/0a1a68885f26cb9f1f5a0713b77b1d5b84dbfb70 I realized simulacron responds to `USE <keyspace>` queries with an empty result.

There should be a capability to respond with a [`set_keyspace`](https://github.com/apache/cassandra/blob/trunk/doc/native_protocol_v5.spec#L702) response.