wait for all sub routines to finish

simple solution for waiting for all go sub routines to
finish before closing Grafana. We would use errGroup
here as well but I dont like spreading context's all
over the place.

closes #10131

pkg/api/http_server.go

@@ -95,7 +95,7 @@ func (hs *HttpServer) Start(ctx context.Context) error {
 
 func (hs *HttpServer) Shutdown(ctx context.Context) error {
 	err := hs.httpSrv.Shutdown(ctx)
-	hs.log.Info("stopped http server")
+	hs.log.Info("Stopped HTTP server")
 	return err
 }