XD-2502 Add embedded Kafka server support

- changed KafkaTestSupport to create and shutdown a standalone Kafka server (and associated ZK instance)
- updated the test to use the embedded broker
XD-2490 - Update to use Reactor 2.0 snapshots
XD-2425: Support RFC5424 SYSLOG Format

JIRA: https://jira.spring.io/browse/XD-2425

Add `--rfc` property; default 3164; can be 3164 or 5424.

Also add `nio` option (false default). nio should be used when many
connections are expected. Previously nio was always used.