issue #565 - Logfile is overwritten when parsedmarc (re)starts (#569)

Do not re-write the log file if already exists. Add a log handler in "append" mode (that should be an implicit value but it's defined explicitly for the visibility).

parsedmarc/cli.py

@@ -1179,9 +1179,7 @@ def process_reports(reports_):
         logger.setLevel(logging.DEBUG)
     if opts.log_file:
         try:
-            log_file = open(opts.log_file, "w")
-            log_file.close()
-            fh = logging.FileHandler(opts.log_file)
+            fh = logging.FileHandler(opts.log_file, "a")
             formatter = logging.Formatter(
                 "%(asctime)s - "
                 "%(levelname)s - [%(filename)s:%(lineno)d] - %(message)s"