Automatic merge from submit-queue

openstack: Support config-drive and improve CurrentNodeName, GetZone

This PR adds support for fetching local instance metadata via config-drive (as well as querying metadata service), and surfaces some additional metadata information (from either source):

- `CurrentNodeName` now returns the OpenStack instance name, rather than the current hostname (they might not be the same)
- `GetZone` includes availability zone label in `FailureDomain`

Thanks to @kiall for a WIP implementation of the latter.