[FIX] runbot: use a logging handler that loves logrotate

When the linux logrotate system rename the runbot logfile used by the
new builder script, the script continue to write in the reotated file.

With this commit, the WatchedFileHandler is used. This handler is
specialy crafted to handle this situation, it detects the file renaming
and automatically changes to the new file that have the old filename.

runbot_builder/builder.py

@@ -6,6 +6,8 @@ import sys
 import threading
 import signal
 
+from logging.handlers import WatchedFileHandler
+
 LOG_FORMAT = '%(asctime)s %(levelname)s %(name)s: %(message)s'
 logging.basicConfig(level=logging.INFO, format=LOG_FORMAT)
 logging.getLogger('odoo.addons.runbot').setLevel(logging.DEBUG)
@@ -80,7 +82,7 @@ def run():
         if dirname and not os.path.isdir(dirname):
             os.makedirs(dirname)
 
-        handler = logging.FileHandler(args.logfile)
+        handler = WatchedFileHandler(args.logfile)
         formatter = logging.Formatter(LOG_FORMAT)
         handler.setFormatter(formatter)
         logging.getLogger().addHandler(handler)