Automatic merge from submit-queue

Add support for Docker for MacOS

With Docker for MacOS [public beta](https://docs.docker.com/docker-for-mac) you don't need docker-machine on MacOS to build kubernetes instead you can use docker "natively". Per Default Docker for MacOS will be installed to `/Applications/Docker.app/Contents/MacOS/Docker` so if Docker for Mac is installed we should use the native version.

I tested it locally with `15.5.0 Darwin Kernel Version 15.5.0`  and Docker version `1.12.0-rc2`