Set --logfile for all kyua invocations

Set --logfile for all kyua invocations

When kyua is called without the --logfile command line option, the log
file is created at a default location which is derived from the HOME
environment variable.  On FreeBSD GitLab CI runners, /home is a
read-only directory and thus kyua invocations not using the --logfile
option fail when HOME is set to something beneath /home.  Set --logfile
to /dev/null for all kyua invocations whose logs are irrelevant in order
to prevent kyua failures caused by HOME being non-writable.

(cherry picked from commit 1bffa602babbc7e76f1ac786e5e35dd7a5d8109f)