ima_violations.sh: Fix log detection

Fix TBROK on systems which does not have /var/log/messages
(any modern distro is using systemd) not auditd installed:

    ima_violations 1 TBROK: log /var/log/messages does not exist (bug in detection?)

Instead TCONF with more meaningful message:

    ima_violations 1 TCONF: log file not found, install auditd

Link: https://lore.kernel.org/ltp/20250114112915.610297-2-pvorel@suse.cz/
Fixes: #372
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>

Author: pevik

testcases/kernel/security/integrity/ima/tests/ima_violations.sh

@@ -23,8 +23,10 @@ setup()
 		PRINTK_RATE_LIMIT=`sysctl -n kernel.printk_ratelimit`
 		sysctl -wq kernel.printk_ratelimit=0
 	fi
-	[ -f "$LOG" ] || \
-		tst_brk TBROK "log $LOG does not exist (bug in detection?)"
+
+	if [ ! -e "$LOG" ]; then
+		tst_brk TCONF "log file not found, install auditd"
+	fi
 	tst_res TINFO "using log $LOG"
 }