Make v2.1 API tests use v2 URLs(test_[a-e].*)

Most v2.1 API tests are using v3 URLs, because there didn't exist
a fake router for v2.1 at the time. However, now the fake router
exists.
This makes v2.1 API tests of use v2 URLs for testing v2.1 API as
v2 compatible API for test_[a-e].*.py.

Partially implements blueprint v2-on-v3-api

Change-Id: I9b5901ca294d10a9ded52603f9cc46155b07009d
Merge "Make v2.1 API tests use v2 URLs(test_[a-e].*)"