Now that we've moved the make update to its own stage, it makes sense to cache
the whole gluon directory between targets because it won't be overwritten by
make update.

Exchange the signing key used by the CI/CD pipeline with a new key.

If build runs through midnight, this avoids different targets having
different build times.

This reverts commit 96535e75.

It is now possible to use usb network cards with a x86 offloader like a
futro, removing the need for a pcie network card