Mess in live-migration compute-manager and drivers code

[Timofey Durakov]

There is _live_migration_cleanup_flags method in compute's manager class which should decide whether it's needed to make cleanup after live-migration is done or not. It accepts 2 params, from doc:
 :param block_migration: if true, it was a block migration
 :param migrate_data: implementation specific data
The problem is that current compute's manager code is libvirt-specific.
It operates values in migrate_data dictionary that valid only for libvirt driver implementation.
This doesn't cause any bug yet because other drivers doesn't implement cleanup method at all.
When anyone decide to implement this live-migration starts to fail. There is no valid ci job to verify that.

live_migration_cleanup_flags - should become hypervisor specific. and we should move it from compute manager to drivers.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/216329

[OpenStack Infra (hudson-openstack)]

Change abandoned by Michael Still (<email address hidden>) on branch: master
Review: https://review.openstack.org/216329
Reason: This code hasn't been updated in a long time, and is in merge conflict. I am going to abandon this review, but feel free to restore it if you're still working on this.

[Markus Zoeller (markus_z) (mzoeller)]

As discussed with Timofey in IRC #nova, this needs to be driven most likely by a blueprint.