Rename Cinder V2 API tests

As http://lists.openstack.org/pipermail/openstack-dev/2017-March/114507.html
we will use the existing Cinder V2 API tests for testing the base
microversion of Cinder V3 API also.
The V2 test classes contained "V2" on these names, and that will be
confusing when using them for the V3 tests.
This patch just renames the V2 tests by removing "V3" from the test
class names.

Change-Id: Ia89f4c1492983aef7d3394a6278c3c3c5fd11529
41 files changed