fetchExtraData = async function(packageNames, force) {
  logger.info("fetchExtraData");
  if (!packageNames) packageNames = [];
  for (let packageName of packageNames) {
    // Verify package
    if (!packageExists(packageName)) {
      logger.error({ pkg: packageName }, "package doesn't exist");
      continue;
    }
    // Load package
    const pkg = await loadPackage(packageName);
    await _fetchPackageInfo(packageName);
    await _fetchPackageScopes(packageName);
    await _fetchRepoInfo(pkg.repo, packageName);
    await _fetchReadme(pkg, packageName);
    await _cacheImage(pkg, packageName, force);
    await _cacheAvatarImage(pkg, packageName, force);
    await _fetchPackageInstallCount(packageName);
  }
}
Fetch package extra data into redis for given packageNames array.
@param {Array} packageNames
@param {Boolean} force