The endpoint of v2.1 API is CURRENT now.
On v2.1 API, a tenant-id is not necessary to be specified on the
URL, that is good for making API calls simple for users.
In addition, the endpoint is different from old v2.0 API.
Then this patch makes the api-site fit for v2.1 format.
Partially implements blueprint api-ref-in-rst
Change-Id: I99224dfa77d64f7800733c1af69a55b3b5c761ac