Add links to API Objects

This patch adds links to the resources, this allows a client to easily
obtain rather than construct resource URIs.

The patch also:
* Add from_rpc_object to convert RPC objects into API object
* Add unittests for the API /chassis/ and /port/
* Change get_all() to return a list of objects instead of a list of UUIDs

Change-Id: I54a7b4846f1e9a76ee5fcb1bc84b5fd2b4fc3d8a
Merge "Add links to API Objects"