pacman-key errors with nightly isos of Arch Linux

tl;dr :

While Setup still running, change tty, Edit /tmp/pacman.conf to add 'SigLevel = Never' somewhere below '[core]', retry the package install step.

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Out of curiosity I tried a nightly iso from here : http://releng.archlinux.org/isos/
The setup fetch the packages but fails to install them (throwing many "key could not be looked up remotely"), warning that "pacman-key --init should probably be run".
Running in vbox , pacman-key --init asks for entropy, usually playing with the system ( mouse, IO ) push the entropy above the needed threshold, but in my case nothing worked. Arch wiki suggests to use rngd from AUR, but the setup isos cannot build from AUR. Reading the output in the logging tty I finally catch the `pacman` command mentionning /tmp/pacman.conf. Adding the 'SigLevel = Never'.

The post-reboot pacman.conf is also using 'SigLevel = Never'.

- build rngd
- pacman-key --init
- switch SigLevel to TrustedOnly or anything that looks paranoid
- install something and see how it goes