allow /etc/hosts /etc/resolv.conf and /etc/hostname to be changed

Fixes #2267
My attempt to fix #2267
Okay, let's revise this sentence to: Note, however, that changes to these files will not be saved by `docker commit`, nor will they be saved during `docker run.` That means they won't be saved in the image, nor will they persist when a container is restarted; they will only "stick" in a running container.