Cache returns the file system path to the cache file storing the ping URLs.

NewPingURLs returns the ping URLs to use.

ReadCachedURLsFile returns a *CachedURLs based on the contents of the file with the given path.

RefreshCache will scrape the manifest url for a dictionary of taskcluster services, and cache the results in file at path.

ScrapePingURLs queries manifestURL to return a manifest of services, which are then queried to fetch ping URLs for taskcluster services.