auth tests should not require admin token

Currently all the v3 auth tests are calling self.post(), which
eventually going through keystone.tests.test_v3.v3_request().
The v3_request method always requires an auth token by default.
But since V3 auth token API is an unprotected API, there's no need
for an auth token in order to make the request.

Change-Id: If65305346c0e5e114fd03e4ba089aa2e3694a8b2
Closes-bug: #1317261
Merge "auth tests should not require admin token"