Reorganize file util functionality (#7848)

* reorganize file util functionality

* fix api test compilation

* fix rebase issue

cmd/platform/server.go

@@ -60,13 +60,17 @@ func runServer(configFileLocation string) {
 	l4g.Info(utils.T("mattermost.working_dir"), pwd)
 	l4g.Info(utils.T("mattermost.config_file"), utils.FindConfigFile(configFileLocation))
 
-	if err := utils.TestFileConnection(); err != nil {
-		l4g.Error("Problem with file storage settings: " + err.Error())
-	}
-
 	a := app.New(app.ConfigFile(configFileLocation))
 	defer a.Shutdown()
 
+	backend, err := a.FileBackend()
+	if err == nil {
+		err = backend.TestConnection()
+	}
+	if err != nil {
+		l4g.Error("Problem with file storage settings: " + err.Error())
+	}
+
 	if model.BuildEnterpriseReady == "true" {
 		a.LoadLicense()
 	}