nixos/oci-containers: check if image exists locally before failing

      text = ''

        ${cfg.backend} rm -f ${name} || true

        ${optionalString (isValidLogin container.login) ''

          # try logging in, if it fails, check if image exists locally

          ${cfg.backend} login \

          ${container.login.registry} \

          --username ${container.login.username} \

          --password-stdin < ${container.login.passwordFile}

          --password-stdin < ${container.login.passwordFile} \

          || ${cfg.backend} image inspect ${container.image} >/dev/null \

          || { echo "image doesn't exist locally and login failed" >&2 ; exit 1; }

        ''}

        ${optionalString (container.imageFile != null) ''

          ${cfg.backend} load -i ${container.imageFile}