Comment 2 for bug 1589460

Libvirt prior to version 1.2.17 doesn't allow block-migration of instances with attached volumes and true live-migration of instances with config drive located on non local-storage both.
This patch changed default config for nova to enable config_drives by default(closes 2 bugs, and 2 related bugs mentioned): https://review.openstack.org/#/c/322132/ At this point it's not possible to fix these issues without changing force_config_drive param in nova. MOS Operator has several possibilities to retain live-migration of volume-backed instances:
- set force_config_drive to True in nova.conf and restart services before booting instance.
- use ceph for ephemerals or set up file-base local storage(e.g. NFS)
- upgrade libvirt to 1.2.17
These options should be mentioned in release notes.
For 10.0 MOS will use Ubuntu 16.04 which ships with libvirt 1.3.1 so it will be possible to use block-migration.