Improved logging in nailgun to simplify debugging process

We have several log files for nailgun app.log and api.log.
Also we have several threads. It was very difficult to find
out which part of log was written by rpc thread and
which by keep alive or web.py thread. Now we can use
standard bash utils to merge two log files and find specific
thread.

* move logs configuration in one place.
  Use single format of time and log format
  for api log and nailgun log.
* add thread logging
* add logging of milliseconds

Implements: blueprint nailgun-improve-logging-for-multithreading-app
Change-Id: I1d8816ad01c39de9602acdba8e99859d0fcd7a57
Merge "Improved logging in nailgun to simplify debugging process"