This patch ensures that the currently broken `thumbor`[1] package builds
and works again.
The following problems were fixed:
* Rather than placing required packages (like `gifsicle` or `exiftool`)
into the build input list, we reference them explicitly where needed
to ensure that the package works after the build without further
installs.
* Skip the `test_redeye_applied` test case which is broken for a while
now.
[1] https://hydra.nixos.org/build/90290998
