Add protocol and port to Ubuntu keyserver address

Without these, the connection to keyserver timed out. And
as the key was not added, apt refused to install lxc-docker.
This solution comes from
http://askubuntu.com/questions/134913/cant-add-repo-keys.

Another way to do this would be adding --force-yes to

  apt-get install -q -y lxc-docker

but this should a lot more secure.