Docker images, again

[Jesús Leganés-Combarro]

It was a pain (Docker itself it is), but finally we have automatically generated nightly Docker images published on DockerHub. They are fully automated too, but testing on the CI server is disabled because SemaphoreCI use Linux kernel 3.13.0 without OverlayFS support, so we'll enable it again when they update their Ubuntu images.

Just a note: there's an incompatibility between NodeOS usage of OverlayFS and Docker aufs default storage driver leading to the full system getting frozen, so you'll need to change it to the overlayfs2 storage driver first.

And now, for it and use NodeOS on your Dockerfiles! :-D