close handlers instead of calling logging.shutdown()

This is to avoid calling .acquire() on a ConcurrentRotatingFileHandler
that has already been closed by the shutdown call.

This doesn't actually fix bug 952929, but it's necessary for the *real*
fix in ConcurrentLogHandler.

Bug: 952929
Change-Id: I642723072f544e5cb21b8a87f490990a27b327d3
Merge "close handlers instead of calling logging.shutdown()" into develop