Make it more clear that we retry transient exceptions
Make it more clear that we retry transient exceptions

* Changed the name of the method to make it clear that it both
  retries and "converts" exceptions.
* Made a separate method of the "retry" part to make it a bit
  easier to understand/read.

See https://github.com/twingly/twingly-url_cache/pull/9#discussion_r260162377

twingly/twingly-url_cache,twingly/twingly-url_cache