Miscellaneous app cleanup (#7594)

* app cleanup

* whoops, forgot a file

* some minor cleanup

* longer container deadline

* defensive checks

app/options.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"github.com/mattermost/mattermost-server/store"
+)
+
+type Option func(a *App)
+
+// By default, the app will use the store specified by the configuration. This allows you to
+// construct an app with a different store.
+//
+// The storeOrFactory parameter must be either a store.Store or func() store.Store.
+func StoreOverride(storeOrFactory interface{}) Option {
+	return func(a *App) {
+		switch s := storeOrFactory.(type) {
+		case store.Store:
+			a.newStore = func() store.Store {
+				return s
+			}
+		case func() store.Store:
+			a.newStore = s
+		default:
+			panic("invalid StoreOverride")
+		}
+	}
+}