Use WatchedFileHandler to avoid copytruncate.

Python logging has a WatchedFileHandler which will do the correct thing
for logrotate when copytruncate is not used. Do this to avoid having
multiple copies of the same log in place. Also, this should avoid a race
where log data is lost between copying and truncating done by logrotate.

Change-Id: Idbbc7869004a03b8f19cfbd81ad07f5584ce1964
Merge "Use WatchedFileHandler to avoid copytruncate."