Check that primary key names are syntactically valid

bin/tests/system/checkconf/bad-primaries-key.conf

@@ -0,0 +1,15 @@
+/*
+ * Copyright (C) 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/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+zone example {
+        type secondary;
+        primaries { 1.2.3.4 key a..b; };
+};