Error: Network timed out while trying to connect to https://index.docker.io/
Solution
# Add nameserver to DNS (probably need to do "sudo su" first)
echo "nameserver 8.8.8.8" > /etc/resolv.conf
# Restart the environment
$ docker-machine restart default
# Refresh your environment settings
$ eval $(docker-machine env default)
I also needed to do this inside the docker-machine:
$ docker-machine ssh default
$ echo "nameserver 8.8.8.8" > /etc/resolv.conf
# Login to Docker VM
$ docker-machine ssh default
# Run DHCP client
$ sudo udhcpc
# Restart docker process
$ sudo /etc/init.d/docker restart