With the events of eventlet removal, Watcher will need
to be adapted to support both modes, eventlet and threading, for
a couple of releases before removing all eventlet code.
This patch adds methods and classes that allow decision engine
modules to create futurist thread pools instead of green thread pools,
based on a environment variable that can be enabled by service.
It moves continuous audit handler instance to decison engine service,
so it can be started together with the main decision engine service.
Adds an environment variable that allows the user to disable
eventlet monkey patching and to use oslo.service threading backend.
Change-Id: I8a8be0a7cebdc44005fd77ec960543828c7da318
Signed-off-by: Douglas Viroel <viroel@gmail.com>