How to make a private registry accessible from inside docker-machine

Working port forwarding for docker registry

#NOTE: our ci machine currently has a weird pfctl rule that I put in place on friday, so port 5000 is not working. 
#Remove that rule, and this should work.
docker-machine create --driver virtualbox --engine-insecure-registry ci:5000 default #Run on all agents/dev boxes

#THE BELOW LINES ONLY APPLY TO THE CI SERVER:
docker-machine stop default
vboxmanage modifyvm "default" --natpf1 "tcp-port5000,tcp,,5000,,5000";
docker-machine start default
docker-machine ssh default "sudo -- sh -c 'echo 10.0.2.2 ci >> /etc/hosts'"

#in the osx machine, change /etc/hosts file entry for 127.0.0.1 localhost to include the ci alias
#In conjunction with the virtualbox port forwarding, this makes it so code docker pushes to the private repo can work on the ci host machine
sed -i '' 's/.*127\.0\.0\.1.*localhost.*/127.0.0.1    localhost   ci/' example-hostsfile 

echo "on other machines, now use the ci machine's network address and put an entry into their /etc/hosts file. Problem solved!"