Surface retriever startup error

[danschultzer]

If you don't set the :default_cldr_backend for :ex_money (I had set for :ex_cldr), the retriever just silently fails start up, and subsequent exchange rates requests fails. Took me a sec to find out it was because the retriever just silently fails.

This change will surfaces any startup error by naively raising the reason, but I think there may be a better way to handle it or format the error. Not really a fan of this solution. I haven't added a test case for it as I couldn't find any tests for the exchange rates supervisor), and again, there's probably a better way to handle the upstart error inside the supervision tree.

The simplest way to test it is to change the test config to:

config :ex_money,
  auto_start_exchange_rates_service: true,
  exchange_rates_retrieve_every: :timer.minutes(1),
  api_module: Money.ExchangeRates.OpenExchangesRates,
  # exchange_rates_retrieve_every: :never,
  # open_exchange_rates_app_id: {:system, "OPEN_EXCHANGE_RATES_APP_ID"},
  # api_module: Money.ExchangeRates.Api.Test,
  log_failure: nil,
  log_info: nil
  # default_cldr_backend: Test.Cldr

The other thing is to figure out why Money wouldn't fall back to the :ex_cldr :default_cldr_backend config for the supervisor.

[kipcole9]

Another great catch.

Having a default CLDR backend is pretty much a requirement for this lib so I think I can check for that in Application.start/0 and raise there if its not configured, or can't be resolved from Cldr.default_backend/0.

I'll work on this later this morning my time. Thanks again.