Make v2.1 API tests use v2 URLs(test_[r-v].*)

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_[r-v].*.py.

Partially implements blueprint v2-on-v3-api

Change-Id: I5388c9e6547e80746af7978642b5dc0c7ad70d0e
Merge "Make v2.1 API tests use v2 URLs(test_[r-v].*)"