add --show-rc option enable "terminating with X status, rc N" output, fixes #351

this is needed for tools like borgweb (or in general: when the rc value / exit status should
be logged for later review or directly seen on screen).

this is off by default, so the output is less verbose (and also does not fail tests which
counts lines).

borg/archiver.py

@@ -571,6 +571,8 @@ Type "Yes I am sure" if you understand this and want to continue.\n""")
         common_parser = argparse.ArgumentParser(add_help=False, prog=prog)
         common_parser.add_argument('-v', '--verbose', dest='verbose', action='store_true', default=False,
                                    help='verbose output')
+        common_parser.add_argument('--show-rc', dest='show_rc', action='store_true', default=False,
+                                   help='show/log the return code (rc)')
         common_parser.add_argument('--no-files-cache', dest='cache_files', action='store_false',
                                    help='do not load/update the file metadata cache used to detect unchanged files')
         common_parser.add_argument('--umask', dest='umask', type=lambda s: int(s, 8), default=RemoteRepository.umask, metavar='M',
@@ -1061,9 +1063,9 @@ def main():  # pragma: no cover
     sys.stderr = io.TextIOWrapper(sys.stderr.buffer, sys.stderr.encoding, 'replace', line_buffering=True)
     setup_signal_handlers()
     archiver = Archiver()
+    msg = None
+    args = archiver.parse_args(sys.argv[1:])
     try:
-        msg = None
-        args = archiver.parse_args(sys.argv[1:])
         exit_code = archiver.run(args)
     except Error as e:
         msg = e.get_message()
@@ -1081,16 +1083,17 @@ def main():  # pragma: no cover
         exit_code = EXIT_ERROR
     if msg:
         logger.error(msg)
-    exit_msg = 'terminating with %s status, rc %d'
-    if exit_code == EXIT_SUCCESS:
-        logger.info(exit_msg % ('success', exit_code))
-    elif exit_code == EXIT_WARNING:
-        logger.warning(exit_msg % ('warning', exit_code))
-    elif exit_code == EXIT_ERROR:
-        logger.error(exit_msg % ('error', exit_code))
-    else:
-        # if you see 666 in output, it usually means exit_code was None
-        logger.error(exit_msg % ('abnormal', exit_code or 666))
+    if args.show_rc:
+        exit_msg = 'terminating with %s status, rc %d'
+        if exit_code == EXIT_SUCCESS:
+            logger.info(exit_msg % ('success', exit_code))
+        elif exit_code == EXIT_WARNING:
+            logger.warning(exit_msg % ('warning', exit_code))
+        elif exit_code == EXIT_ERROR:
+            logger.error(exit_msg % ('error', exit_code))
+        else:
+            # if you see 666 in output, it usually means exit_code was None
+            logger.error(exit_msg % ('abnormal', exit_code or 666))
     sys.exit(exit_code)