ktest: Fix bug where the test would not end after failure

The config STOP_AFTER_FAILURE is the number of seconds to continue
the test when a failure is detected. This lets the monitor record
more data to the logs and console that may be helpful in solving
the bug that was found.

But the test had a bug. If the failure caused multiple
"Call Trace" stack dumps, the start time to compare the
STOP_AFTER_FAILURE would constantly be reset. Only update the start
time at the first "Call Trace" instance.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

tools/testing/ktest/ktest.pl

@@ -804,7 +804,7 @@ sub monitor {
 	}
 
 	if ($full_line =~ /call trace:/i) {
-	    if (!$skip_call_trace) {
+	    if (!$bug && !$skip_call_trace) {
 		$bug = 1;
 		$failure_start = time;
 	    }