vlog test: Disable default syslog logger

Disable the syslog logger in case on Windows, '/dev/log' doesn't exist.
Seems like on Python34 a default handler is added to the logger and it prints
even if no handler is set by us.

Signed-off-by: Paul-Daniel Boca <pboca@cloudbasesolutions.com>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>

python/ovs/vlog.py

@@ -301,6 +301,7 @@ def add_syslog_handler(facility=None):
         # If there is no infrastructure to support python syslog, increase
         # the logging severity level to avoid repeated errors.
         if not os.path.exists("/dev/log"):
+            logger.disabled = True
             logger.setLevel(logging.CRITICAL)
             return