Create overlayfs-based IUKs v2 for the test suite

Originally created by @intrigeri on #17440 (Redmine)

See 5f13cb87 for details.

Feature Branch: feature/8415-overlayfs+force-all-tests, master

Edited May 15, 2020 by intrigeri

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