Make tails-iuk support overlayfs
The IUK creation process and its test suite both rely on aufs now. Whenever we’ll be ready to use overlayfs instead everywhere else, these two pieces of code will need to support overlayfs too. A first step could be to make this configurable, support both, so that there’s less of a flag day.
Feature Branch: iuk:feature/9373-overlayfs
Parent Task: #8415 (closed)