Make SQLite default for new installations (#1529)

* Make SQLite default for new installations

* if var is not set, return empty string

this allows getStoreEngineFromDatadir to detect json store files

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Co-authored-by: Maycon Santos <mlsmaycon@gmail.com>

management/server/sqlite_store.go

@@ -485,7 +485,11 @@ func (s *SqliteStore) SaveUserLastLogin(accountID, userID string, lastLogin time
 
 // Close is noop in Sqlite
 func (s *SqliteStore) Close() error {
-	return nil
+	sql, err := s.db.DB()
+	if err != nil {
+		return err
+	}
+	return sql.Close()
 }
 
 // GetStoreEngine returns SqliteStoreEngine