Scheduler that allows routing some calls to one driver and others to another.
This scheduler was originally used to deal with both compute and volume. But is now used for openstack extensions that want to use the nova-scheduler to schedule requests to compute nodes but provide their own manager and topic.
https://bugs.launchpad.net/nova/+bug/1009681
Bases: nova.scheduler.driver.Scheduler
A scheduler that holds multiple sub-schedulers.
This exists to allow flag-driven composibility of schedulers, allowing third parties to integrate custom schedulers more easily.