test: fix spurious EADDRINUSE in test-https-strict

test-https-strict sometimes fails with EADDRINUSE in CI. Remove use of
common.PORT to make the test resistant from side effects from other
tests that may have not freed up the port.

PR-URL: https://github.com/nodejs/node/pull/7024


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>