The API specifications were moved out of the specs repo and into the
api-ref directory of the main keystone repo[1]. This patch updates some
of the straggler links in the configuration docs that still referenced
the old location.
[1] https://review.openstack.org/#/c/342399/
Change-Id: I883cfb4ab8b65873286f46194a8c8ccd7af97dd2