Add a node

A node is a physical server that runs VMs for the engine. It needs no installation of its own: it boots from the engine over the network, and joins.

Outline

1. The hardware - what a node needs: virtualisation support, a network card on the engine's node network, and local disk if VMs are to keep theirs there.
2. Booting it - set it to boot from the network; the engine hands it its system.
3. Joining - it appears on the Nodes tab, and starts taking VMs.
4. Looking after it - maintenance, moving its VMs away, and sleep.