Spot/preemptible instance

[Tobias Rydberg]

To support feature similar to preemptible instance in AWS. The development goal is to have Nova exposes the API so that other systems could build on top of it

"There was also a BOS forum session discussing this, although hosted by Scientific WG: https://etherpad.openstack.org/p/BOS-forum-advanced-instance-scheduling (ttsiouts) http://openstack-in-production.blogspot.ie/2018/02/maximizing-resource-utilization-with.html"

References:
"old nova spec at https://review.openstack.org/#/c/104883/, there is a new spec John Garbutt working on at https://review.openstack.org/#/c/438640/.

(mriedem): Queens PTG notes: https://etherpad.openstack.org/p/nova-ptg-queens (L273)"

[Matt Riedemann (mriedem)]

Current nova spec:

https://review.openstack.org/#/c/554212/

[Theodoros Tsioutsias (ttsiouts)]

Full list of proposed changes:

[Spec] Add PENDING vm state: https://review.openstack.org/#/c/554212/
  - https://review.openstack.org/#/c/566473/
  - https://review.openstack.org/#/c/566470/ (most probably obsolete)

[Spec] Enable rebuild for instances in cell0: https://review.openstack.org/#/c/554218/
  - https://review.openstack.org/#/c/570201/
  - https://review.openstack.org/#/c/570202/
  - https://review.openstack.org/#/c/570203/