Follow-up fix for parsing non-utf8 chars

Previous attempt to fix this in commit 7290540 ("tap13: fix parsing
non-utf8 chars") didn't take into account the hung test reporter, which
also reads the result file in order to report how many lines into the
result the test hung. Fix this as well.

Closes #442

listeners.py

@@ -459,7 +459,7 @@ def process_timeout(self, delta_seconds):
             result_file = task.task_tmp_result
             result_file_summary = '(no result file {})'.format(result_file)
             if os.path.exists(result_file):
-                with open(result_file, 'r') as f:
+                with open(result_file, 'r', encoding='utf-8', errors='replace') as f:
                     lines = sum(1 for _ in f)
                     result_file_summary = 'at {}:{}'.format(result_file,
                                                             lines)