Add provision_updated_at to node's resource

This patch is a follow up of e7c4e1882b0bee2a984db7e24e8bd52d008b984b,
it's adding the new provision_updated_at field to the node's resource
body so that it can be retrieved by GET request.

Change-Id: I2091e8de6d9d3df3299358a254aa67e846ccfb47
Merge "Add provision_updated_at to node's resource"