Clean up JSON home API

Fixes dolphm's comments from:
  - https://review.openstack.org/#/c/109881/

And my issue addressed here:
  - https://review.openstack.org/#/c/111576/6/keystone/assignment/routers.py

Change-Id: I81e2aab1f0e8dfd06a3aa95cb7270e3b5684043d