compute: use live_migration_tunnelled
In a previous patch [1], we added support for VIR_MIGRATE_TUNNELLED when
doing VM shared storage.
In Nova Mitaka [2] [3], we have now a parameter called
'live_migration_tunnelled' to whether or not use tunnelled migration.
It replaces 'block_migration_flag' and 'live_migration_flag' that are
both deprecated.
[1] https://review.openstack.org/#/c/286584/
[2] https://review.openstack.org/#/c/263436/
[3] https://review.openstack.org/#/c/263434/
Change-Id: I8b199b6e72c80b2df7b679e0a20e39f8400d0478