Regression introduced in 736848723e.
This commit most certainly hasn't been tested with sandboxing enabled
and breaks not only pullImage but also the docker-tools NixOS VM test
because it doesn't find it's certificate path and also relies on
/var/tmp being there.
Fixing the certificate path is the easiest one because it can be done
via environment variable.
I've used overrideAttrs for changing the hardcoded path to /tmp (which
is available in sandboxed builds and even hardcoded in Nix), so that
whenever someone uses Skopeo from all-packages.nix the path is still
/var/tmp.
The reason why this is hardcoded to /var/tmp can be seen in a comment in
vendor/github.com/containers/image/storage/storage_image.go:
Do not use the system default of os.TempDir(), usually /tmp, because
with systemd it could be a tmpfs.
With sandboxed builds this isn't the case, however for using Nix without
NixOS this could turn into a problem if this indeed is the case.
So in the long term this needs to have a proper solution.
In addition to that, I cleaned up the expression a bit.
Tested by building dockerTools.examples.nixFromDockerHub and the
docker-tools NixOS VM test.
Signed-off-by: aszlig <aszlig@nix.build>
Cc: @nlewo, @Mic92, @Profpatsch, @globin, @LnL7
42a0b11450