Fix the log prefix after a thread exits
Fix the log prefix after a thread exits

twisted.python.context is not asynchronous, meaning it gets lost if
processing is delegated to a thread and that thread exits. Get around
that by restoring the log context ourselves.

Change-Id: I058e4d9fa592a314ec04b541a10cdda294c70f3b
Reviewed-by: Fred Barnes <a457b66771fa7031f08927d92d89014c238c08f7@morganstanley.com>

quattor/aquilon,quattor/aquilon,quattor/aquilon