nixos stage-1: wait for resume devices to appear

[abbradar]

Motivation for this change

Fixes #8803

Things done

• Tested using sandboxing
  (nix.useChroot on NixOS,
  or option build-use-chroot in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

Tested with tests.hibernate.x86_64-linux. This needs further testing: I can't test this in situations where the delay is actually needed.

[mention-bot]

@abbradar, thanks for your PR! By analyzing the annotation information on this pull request, we identified @edolstra, @7c6f434c and @wmertens to be potential reviewers

[wmertens]

Could you make this commit be minimal? Looks like you moved some functions around so it's hard to tell what changed. If you really want to move those, do it in a separate "cleanup" commit.

[abbradar]

@wmertens Done, thanks for the remark!

[wmertens]

Alright, looks fine to me. Should not impact builds and should not break working things, so merging.