MM-14143 config cleanup final (#10374)

* TestGetLicenseFileFromDisk: avoid using fileutils.FindConfigFile

* config: abstract config-related file access, extend memory store

* simplify config validate to avoid file knowledge

* fix relative file tests

* cluster: fix ConfigChanged event

The old and new configurations were swapped when notifying the enterprise code of configuration changes, creating needless instability in propagating config updates across a cluster.

* config/database: ignore duplicates

* test cleanup

* remove unnecessary Save() in test

app/admin.go

@@ -17,6 +17,7 @@ import (
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/services/mailservice"
 	"github.com/mattermost/mattermost-server/utils"
+	"github.com/pkg/errors"
 )
 
 func (a *App) GetLogs(page, perPage int) ([]string, *model.AppError) {
@@ -162,7 +163,7 @@ func (a *App) GetEnvironmentConfig() map[string]interface{} {
 
 func (a *App) SaveConfig(newCfg *model.Config, sendConfigChangeClusterMessage bool) *model.AppError {
 	oldCfg, err := a.Srv.configStore.Set(newCfg)
-	if err == config.ErrReadOnlyConfiguration {
+	if errors.Cause(err) == config.ErrReadOnlyConfiguration {
 		return model.NewAppError("saveConfig", "ent.cluster.save_config.error", nil, err.Error(), http.StatusForbidden)
 	} else if err != nil {
 		return model.NewAppError("saveConfig", "app.save_config.app_error", nil, err.Error(), http.StatusInternalServerError)
@@ -177,7 +178,7 @@ func (a *App) SaveConfig(newCfg *model.Config, sendConfigChangeClusterMessage bo
 	}
 
 	if a.Cluster != nil {
-		err := a.Cluster.ConfigChanged(newCfg, oldCfg, sendConfigChangeClusterMessage)
+		err := a.Cluster.ConfigChanged(oldCfg, newCfg, sendConfigChangeClusterMessage)
 		if err != nil {
 			return err
 		}