* make it possible to use external Aeron media driver, #20588
* on my machine the MaxThroughputSpec maxed out all 8 cores completely,
and when using external media driver it is much better and easier to
find the actual bottlenecks
* aeron.properties for external media driver
* Automatic port selection when port 0 configured
* Combine remoting and artery SunnyWeatherSpec
* Default to port 0 for artery in MultiNodeSpec.nodeConfig