Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/remove-cast-to-schedule-run-instance.

Description:

In Havana it became possible to query the scheduler for a list of hosts to provision an instance on.  Now we should switch the booting of a new instance to use that new query rather than proxy through the scheduler as is currently done.  

This is in preparation for moving towards something like TaskFlow which would allow Nova to stop and resume multi step operations.  By moving away from run_instance we are consolidating the provisioning logic between the conductor and compute manager.  This clears up the responsibilities of the scheduler so that work there can focus on scheduling improvements.

Specification URL (additional information):

None