Logs provider name on startup

If invalid provider is specified, stop and error out

fixes #895

providers/providers.go

@@ -46,7 +46,9 @@ func New(provider string, p *ProviderData) Provider {
 		return NewNextcloudProvider(p)
 	case "digitalocean":
 		return NewDigitalOceanProvider(p)
-	default:
+	case "google":
 		return NewGoogleProvider(p)
+	default:
+		return nil
 	}
 }