docker-tools: add a test for permissions issues with AUFS/overlay

docker# [   11.054736] d24d6cdd57c9[763]: /bin/bash: error while loading
shared libraries: libreadline.so.7: cannot open shared object file:
Permission denied
docker# /bin/bash: error while loading shared libraries:
libreadline.so.7: cannot open shared object file: Permission denied
docker: exit status 127
docker: output:
error: command `docker run --rm -u 1000:1000 bash /bin/bash --version'
did not succeed (exit code 127)
command `docker run --rm -u 1000:1000 bash /bin/bash --version' did not
succeed (exit code 127)

nixos/tests/docker-tools-overlay.nix

@@ -0,0 +1,32 @@
+# this test creates a simple GNU image with docker tools and sees if it executes
+
+import ./make-test.nix ({ pkgs, ... }:
+{
+  name = "docker-tools-overlay";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ lnl7 ];
+  };
+
+  nodes = {
+    docker =
+      { config, pkgs, ... }:
+      {
+        virtualisation.docker.enable = true;
+        virtualisation.docker.storageDriver = "overlay";  # defaults to overlay2
+      };
+  };
+
+  testScript =
+    ''
+      $docker->waitForUnit("sockets.target");
+
+      $docker->succeed("docker load --input='${pkgs.dockerTools.examples.bash}'");
+      $docker->succeed("docker run --rm ${pkgs.dockerTools.examples.bash.imageName} bash --version");
+
+      # Check if the nix store has correct user permissions depending on what
+      # storage driver is used, incorrectly built images can show up as readonly.
+      # drw-------  3 0 0   3 Apr 14 11:36 /nix
+      # drw------- 99 0 0 100 Apr 14 11:36 /nix/store
+      $docker->succeed("docker run --rm -u 1000:1000 ${pkgs.dockerTools.examples.bash.imageName} bash --version");
+    '';
+})