New block to run on next boot

[ericraymond]

The general idea is that we may need to have a reboot or two during the initial setup process. RASPAP has this as qa requirement, for example. This would essentially be similar to on every boot but would only run once with some ordering to say which block (if more than one block) runs first.

One other benefit of this is that it allows additional, incremental setup to be performed without starting from scratch (e.g. ,via update, not write).