Add 'location' and 'state' attributes for Rack

The location attribute appears on latest wireframes and is seems to be used to determine the physical location of the Rack in datacenter. In case of Tuskar, this is just an extra String(128) attribute.

The state attribute also appears in the latest wire frames and it indicate in what 'state' the Rack currently is (like. 'unprovisioned').

Everything should be covered by unit tests.