Move all volume v2 service client unit tests to v3 dir

This patch set is a follow up to https://review.openstack.org/#/c/578993/
which moved the volumes v2 client into v3 and consolidated the
tests.

This patch set does the same for the remaining v2 service clients,
all of which are deprecated. Specifically:

* if there is no v3 version, move the v2 to v3 and change the
  service client import path from v2 to v3
* if there is a v3 version, move the v2 tests into v3 test module
  and delete the v2 test file to avoid test overlap

Change-Id: I2a999a9c41e6b5cd7e2b7b17e338bd697cb262b1
16 files changed