According to guideline from API-WG [1], the version discovery protocol
requires a GET on '/' return a dictionary containing 'versions', whose
value is a list of supported versions. Under each version record, there
could be multiple 'links'. This patch tunes the root controller to
better align with this guideline.
[1] http://git.openstack.org/cgit/openstack/api-wg/tree/guidelines/
microversion_specification.rst#n130
Change-Id: I6834310e6d4e7e14a7720f6577890757fe4dca21
4293e4061f