Multiple service launchers and eventlet backdoor initialization

[Mark McLoughlin]

In service.Launcher, we do:

 class Launcher(object):
    def __init__(self):
        eventlet_backdoor.initialize_if_enabled()

and this spawns a greenthread listening on a configured port

This will break if you use Launcher multiple times (the port will be in use)

Also, the spawned thread isn't managed at all - e.g. stopped at shutdown time

[Matthew Treinish (treinish)]

I have a patch that address this issue (at least the first one) up for review in nova:

https://review.openstack.org/#/c/15446/

The fix is nova specific in that it adds a new port option for each nova service that will use backdoors.