t_client: Allow to force FAIL on prerequisite fails

t_client: Allow to force FAIL on prerequisite fails

In automated tests we want the build to fail if the
worker node is configured incorrectly.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220722134902.22092-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24723.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 79932b94513303567fdd5d1c4e0abb79e6642b6e)