This makes us actually capable of sending migrate_data objects
over the wire and handles all the compatibility work to tolerate
older nodes without this support.
Note this also fixes a bug in the libvirt migration data
object where the serial console field should be nullable
(per existing code) but wasn't. Since this is the patch that
actually lets this object be sent over the wire, we can update
the definition and the hash without needing a version bump.
Related to blueprint objectify-live-migrate-data
Change-Id: I8ad7a91910e269c27bc74389a9d4d2c7388313d6
2d7a851199