dockerTools: Use lib.getExe and getExe' to get executable paths (#477896)

      # A user is required by nix

      # https://github.com/NixOS/nix/blob/9348f9291e5d9e4ba3c4347ea1b235640f54fd79/src/libutil/util.cc#L478

      export USER=nobody

      ${buildPackages.nix}/bin/nix-store --load-db < ${

      ${lib.getExe' buildPackages.nix "nix-store"} --load-db < ${

        closureInfo { rootPaths = contentsList; }

      }/registration

      # Reset registration times to make the image reproducible

      ${buildPackages.sqlite}/bin/sqlite3 nix/var/nix/db/db.sqlite "UPDATE ValidPaths SET registrationTime = ''${SOURCE_DATE_EPOCH}"

      ${lib.getExe buildPackages.sqlite} nix/var/nix/db/db.sqlite "UPDATE ValidPaths SET registrationTime = ''${SOURCE_DATE_EPOCH}"

      mkdir -p nix/var/nix/gcroots/docker/

      for i in ${lib.concatStringsSep " " contentsList}; do

        mkdir -p $out

        tarhash=$(tar -C layer --hard-dereference --sort=name --mtime="@$SOURCE_DATE_EPOCH" -cf - . |

                    tee -p $out/layer.tar |

                    ${tarsum}/bin/tarsum)

                    ${lib.getExe tarsum})

        cat ${baseJson} | jshon -s "$tarhash" -i checksum > $out/json

        # Indicate to docker that we're using schema version 1.0.

  # "#!/usr/bin/env executable" shebang.

  usrBinEnv = runCommand "usr-bin-env" { } ''

    mkdir -p $out/usr/bin

    ln -s ${coreutils}/bin/env $out/usr/bin

    ln -s ${lib.getExe' coreutils "env"} $out/usr/bin

  '';

  # This provides /bin/sh, pointing to bash (interactive).

  # The use of bash (interactive) here is intentional to support cases like `docker run -it <image_name>`, so keep these use cases in mind if making any changes to how this works.

  binSh = runCommand "bin-sh" { } ''

    mkdir -p $out/bin

    ln -s ${bash}/bin/bash $out/bin/sh

    ln -s ${lib.getExe bash} $out/bin/sh

  '';

  # This provides the ca bundle in common locations

      #

      # https://github.com/NixOS/nix/issues/6379

      homeDirectory ? "/build",

      shell ? bash + "/bin/bash",

      shell ? lib.getExe bash,

      command ? null,

      run ? null,

    }: