migration: Inactivate images after .save_live_complete_precopy()

migration: Inactivate images after .save_live_complete_precopy()

Block migration may still access the image during its
.save_live_complete_precopy() implementation, so we should only
inactivate the image afterwards.

Another reason for the change is that inactivating an image fails when
there is still a non-device BlockBackend using it, which includes the
BBs used by block migration. We want to give block migration a chance to
release the BBs before trying to inactivate the image (this will be done
in another patch).

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>