Register agent schedulers options in one place

Currently agent schedulers options are defined in neutron.scheduler and
every plugin that supports scheduling should register them individually.
It is reasonable to define and register options in one place - agentschedulers_db.

Fixes NeutronManagerTestCase when running separately by importing missing config option

Fixes bug 1198904

Change-Id: Ia9c1ad3fb4b71796401ef5507f741f3cc024a4da
Add status description field for lbaas objects

Fixes bug 1166925

Change-Id: I44d936afd8cd531a786c09c38bbc4702737ce99c
Merge "Add status description field for lbaas objects"
Merge "Register agent schedulers options in one place"