rebuild or replace scaleway boxes (scw-arm-*)

the boxes we have at scaleway (scw-arm-ams-01 and scw-arm-par-01) are "old" according to scaleway. this leads to various problems, documented in their ticket tracker:

• #WJVJ-9718-KIPG - machines do not reboot unattended
• #GHYX-4885-QWLA - kernel not used

Their newer platform allows us to run our own kernels, and also handles reboots better. Right now scq-arm-ams-01 is down because I can't figure out how to reboot it properly, for example.

This would require reinstalling the machines and setting them up as build boxes again.