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
dcbeee67d9