Document and/or create a small 'AddNodeCfg' process & tool

[ssenator]

Current process is as follows:

1. Add an entry into clusters/<cluster-id>/common/etc/{hosts,ethers} for the new host picking a unique
   IP and MAC address
2. Put in a corresponding entry into clusters/<cluster-id>/Vagrantfile.<cluster-id>.nodes
3. Add an entry into clusters/<cluster-id>/common/etc/slurm.conf, for the node itself and whichever partition(s) are appropriate.
4. Update clusters/<cluster-id>/cfg/<new-node>/requires/<pre-requisite-nodes>/<pre-requisite-svcs> up