Ensure that all unit tests use unbuffered stdout and stderr

Ensure that all unit tests use unbuffered stdout and stderr

stderr is normally always unbuffered but stdout can be buffered. Especially,
when stdout is redirected it will become buffered while it is normally
unbuffered when connected to a terminal. This mean that if the unit exits
prematurely, the output in the buffered output will be lost.

As the unit test x_msg mock implementation prints even fatal on stdout
we ensure with this setup method that stdout is also unbuffered.

Change-Id: I5c06dc13e9d8ab73997f79b13c30ee8949e5e993
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20240123104358.495517-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28122.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>