Fixes bug with display message logic due to deprecating GenericSource. Also added more test cases to cover a bunch more edge cases

command/alloc_status.go

@@ -440,8 +440,7 @@ func buildDisplayMessage(event *api.TaskEvent) string {
 		desc = event.DriverMessage
 	case api.TaskLeaderDead:
 		desc = "Leader Task in Group dead"
-	case api.TaskGenericMessage:
-		event.Type = event.GenericSource
+	default:
 		desc = event.Message
 	}