Extend the 'doth' system test with Strict/Mutual TLS checks

This commit extends the 'doth' system test with a set of Strict/Mutual
TLS related checks.

This commit also makes each doth NS instance use its own TLS
certificate that includes FQDN, IPv4, and IPv6 addresses, issued using
a common Certificate Authority, instead of ad-hoc certs.

Extend servers initialisation timeout to 60 seconds to improve the
tests stability in the CI as certain configurations could fail to
initialise on time under load.

bin/tests/system/doth/get_openssl_version.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python
+
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# 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 https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+import ssl
+version = ssl.OPENSSL_VERSION_INFO
+print(version[0], version[1], version[2])