Rebase isotesters' custom QEMU on 1:2.8+dfsg-4

We currently run 1:2.8+dfsg-3.0tails1 and a newer package was uploaded to Debian and will make it into testing shortly.

Original created by @intrigeri on 12468 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information