Allow setting max downtime for libvirt live migrations

[Chris St. Pierre]

As of libvirt 1.2.9, the maximum downtime for a live migration is tunable during a migration, so it doesn't require any threading foolishness. We should make this configurable in nova.conf so that large instances can be migrated across relatively smaller network pipes.

[Christopher Yeoh (cyeoh-0)]

Probably better just to submit a blueprint for this (might qualify as trivial so not need a spec).

[Chris St. Pierre (stpierre)]

Blueprint registered: https://blueprints.launchpad.net/nova/+spec/set-live-migration-max-downtime

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/141826

[OpenStack Infra (hudson-openstack)]

Change abandoned by Chris St. Pierre (<email address hidden>) on branch: master
Review: https://review.openstack.org/141826
Reason: Actually, it occurs to me that admins can just use the live_migration_flag to set this themselves. No patch necessary. Yay!

[Davanum Srinivas (DIMS) (dims-v)]

Looks like Chris does not need this anymore :)