Rather than relying on carefully avoiding touching the 9P-mounted /nix/store, we instead install a small NixOS system, similar to the installer tests, and boot from that. This avoids the various pitfalls associated with trying to unsuspend properly and trades off a bunch of boilerplate for what will hopefully be a more reliable test. Additionally, this test now actually tests booting the system using a bootloader, rather than the previous method of just booting the kernel directly.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at https://nixos.org/nixos and in the manual in doc/manual.