Add java16 unix socket support - #1627

Good changes! Random aside, is there a reason why the docker-java dependency depends on both netty and jersey, especially when under the https://github.com/docker-java/docker-java/blob/master/docs/transports.md transports page it says apache is the most stable?

@Sineaggi docker-java is a meta package, and, starting with #1237, it is possible to depend on api + core + your transport of choice.

Also, as per the link you shared, any transport that is not marked as "Long term support" most probably will be removed in the next major version.

With the advent of java 17 fast approaching, I'd love to see users of docker-java being able to make use of this. Are there any concerns with getting this merged?

@Sineaggi I just applied a bit of polishing, successfully tested locally with JDK16 and will merge in a moment. Thank you! 👍