Introduce Pending VM state for OpenStack Compute (nova)

This feature adds support for the PENDING server state. Instead of setting a server to the ERROR state when the Placement returns no valid hosts for the requested server, the PENDING state is used if the operator wishes so. This will allow the execution of subsequent actions transparently to the end user.

Enable Rebuild for Instances in cell0 for OpenStack Compute (nova)

This spec summarizes the changes needed to enable the rebuilding of instances that failed during creation.

Preemptible instances support for OpenStack Compute (nova)

Add support for preemptible instances. A preemptible instance is a special kind of instance that can be terminated (or suspended) automatically by the system if there are no resources available to satisfy a non-spot request.