[Currency support] Activate multi-currencies support (prebid#894)

This CL is the last piece to activate currency conversion support in
PBS. It activates currency support per default.

Currency rates will be fetched once per hour (PrebidJS file is updated
once a day).

Issue: prebid#280

config/config.go

@@ -600,7 +600,7 @@ func SetupViper(v *viper.Viper, filename string) {
 	v.SetDefault("gdpr.timeouts_ms.init_vendorlist_fetches", 0)
 	v.SetDefault("gdpr.timeouts_ms.active_vendorlist_fetch", 0)
 	v.SetDefault("currency_converter.fetch_url", "https://cdn.jsdelivr.net/gh/prebid/currency-file@1/latest.json")
-	v.SetDefault("currency_converter.fetch_interval_seconds", 0) // #280 Not activated for the time being
+	v.SetDefault("currency_converter.fetch_interval_seconds", 1800) // fetch currency rates every 30 minutes
 	v.SetDefault("default_request.type", "")
 	v.SetDefault("default_request.file.name", "")
 	v.SetDefault("default_request.alias_info", false)

config/config_test.go

@@ -24,6 +24,8 @@ func TestDefaults(t *testing.T) {
 	cmpInts(t, "host_cookie.ttl_days", int(cfg.HostCookie.TTL), 90)
 	cmpStrings(t, "datacache.type", cfg.DataCache.Type, "dummy")
 	cmpStrings(t, "adapters.pubmatic.endpoint", cfg.Adapters[string(openrtb_ext.BidderPubmatic)].Endpoint, "http://hbopenbid.pubmatic.com/translator?source=prebid-server")
+	cmpInts(t, "currency_converter.fetch_interval_seconds", cfg.CurrencyConverter.FetchIntervalSeconds, 1800)
+	cmpStrings(t, "currency_converter.fetch_url", cfg.CurrencyConverter.FetchURL, "https://cdn.jsdelivr.net/gh/prebid/currency-file@1/latest.json")
 }
 
 var fullConfig = []byte(`