Set a LMDB mapsize and also provide a config option to control it (#44954)

(cherry picked from commit 241b49e611)

bin/tests/system/checkconf/bad-lmdb-mapsize-unlimited.conf

@@ -0,0 +1,11 @@
+/*
+ * Copyright (C) 2016  Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+options {
+	lmdb-mapsize unlimited;
+};