Update migrate_volume API to use versionedobjects

Update migrate_volume API to use versionedobjects

The following patch updates migrate_volume,
migrate_volume_completion, and update_migrated_volume
APIs to use volume versionedobjects.  Changes were
made to be backwards compatible with older RPC clients.
It only includes changes to the core cinder code.
Changes in the drivers are left to each driver
maintainer to update.

Note that this patch DOES NOT try to use object dot
notation everywhere, since it would increase the
size of the patch.  Instead, it will be done in
subsequent patches.

Change-Id: I21fe68193c934a7ef3688274ab35f664a08cac7e
Partial-Implements: blueprint cinder-objects
Closes-Bug: #1521085