Improved bulkload error handling (#8491)

* log the config file path used by the server on startup

* return an err if the bulk import command fails

* log the underlying errors that occur when importing

The code assumed all errors meant a missing resource, but it's possible
something else is at fault. Including the error helps pinpoint that more
readily.

app/config.go

@@ -54,6 +54,7 @@ func (a *App) LoadConfig(configFile string) *model.AppError {
 	a.configFile = configPath
 
 	utils.ConfigureLog(&cfg.LogSettings)
+	l4g.Info("Using config file at %s", configPath)
 
 	a.config.Store(cfg)