Sync revert and finish resize on instance.uuid

We need to make sure we sync the state of the instance the same way we
do for do_confirm_resize. Previously, we were not syncing the instance
on revert or finish resize. We do this so that we can update the
migration and instance resize update orders. Previously if you set
resize_confirm_window to some small value, your resized instance could
go into error state because the periodic task was run after the
migration was updated but before the instance object was updated. This
change makes it so the instance is always updated before the migration.

Change-Id: Iaad1a05864b2b46180cadf16198b0fd8583c6703
Closes-Bug: 1326778
VMware: refactor get_datastore_ref_and_name

Update vm_util.get_datastore_ref_and_name to use Datastore class,
renamed it to get_datastore, remove vm_util.DSRecord along the way.

partial blueprint vmware-spawn-refactor

Change-Id: Ib3308870c09344036c4f330a48513581f5771246
Merge "Sync revert and finish resize on instance.uuid"
Merge "VMware: refactor get_datastore_ref_and_name"