Fail vs. fatal on store startup (#24170)

If the store fails to initialize (e.g. run a migration), it would `log.Fatal` and then `os.Exit`. Unfortunately, this trips up `TestMain`, which happily keeps running tests, now guaranteed to fail.

Avoid this by instead returning an error from the store initialization, handling appropriately at the layer above.

server/channels/testlib/helper.go

@@ -118,7 +118,12 @@ func (h *MainHelper) setupStore(withReadReplica bool) {
 
 	h.SearchEngine = searchengine.NewBroker(config)
 	h.ClusterInterface = &FakeClusterInterface{}
-	h.SQLStore = sqlstore.New(*h.Settings, nil)
+
+	var err error
+	h.SQLStore, err = sqlstore.New(*h.Settings, nil)
+	if err != nil {
+		panic(err)
+	}
 	h.Store = searchlayer.NewSearchLayer(&TestStore{
 		h.SQLStore,
 	}, h.SearchEngine, config)
@@ -130,7 +135,12 @@ func (h *MainHelper) ToggleReplicasOff() {
 	}
 	h.Settings.DataSourceReplicas = []string{}
 	lic := h.SQLStore.GetLicense()
-	h.SQLStore = sqlstore.New(*h.Settings, nil)
+
+	var err error
+	h.SQLStore, err = sqlstore.New(*h.Settings, nil)
+	if err != nil {
+		panic(err)
+	}
 	h.SQLStore.UpdateLicense(lic)
 }
 
@@ -140,7 +150,13 @@ func (h *MainHelper) ToggleReplicasOn() {
 	}
 	h.Settings.DataSourceReplicas = h.replicas
 	lic := h.SQLStore.GetLicense()
-	h.SQLStore = sqlstore.New(*h.Settings, nil)
+
+	var err error
+	h.SQLStore, err = sqlstore.New(*h.Settings, nil)
+	if err != nil {
+		panic(err)
+	}
+
 	h.SQLStore.UpdateLicense(lic)
 }