confd: reduce noise during normal config reload

During a normal configuration update, done via write to temp file and
rename, this is what confd logs (slightly edited for clarity):

2012-12-14 01:05:53: ganeti-confd INFO Loaded new config, serial 21866
2012-12-14 01:06:18: ganeti-confd INFO File lost, trying to re-establish notifier
2012-12-14 01:06:18: ganeti-confd INFO Loaded new config, serial 21867
2012-12-14 01:07:09: ganeti-confd INFO File lost, trying to re-establish notifier
2012-12-14 01:07:09: ganeti-confd INFO Loaded new config, serial 21868

Since this happens always, we should demote the "File lost" messages
to debug level, to keep the logs more clear.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Bernardo Dal Seno <bdalseno@google.com>