(cherry picked from commit 13fce878)

Conflicts:
	stack/slapos.cfg

This was intended in 795cedcf, but it should not be needed to revert there.

(cherry picked from commit c85f3c63)

Also put back certificates on software release url.

This is the only remote url which is going to be trusted outside of buildout.

Fetching list of keys over the network from non signed url has no sense.

https://github.com/hexagonit/hexagonit.recipe.download/commit/9eeede0b231fc44757be9cb54eed7f245fc7ede4
https://github.com/hexagonit/hexagonit.recipe.download/commit/e2985968d0fbe5672183d04478bb0fe9b641a351

(cherry picked from commit c0180cf9)

(cherry picked from commit bd8ac231)

(cherry picked from commit c0180cf9)

(cherry picked from commit bd8ac231)

This version forces h.r.download to clean its own mess in /tmp.