Fix volume v2 capabilities/scheduler-stats tests to test v2 APIs

Currently capabilities/scheduler-stats tests for volume v2 APIs are
making call to v1 API instead of v2. Because api_version is missing in
respective service clients.

This commit fix the issue by specifying the api_version as v2 on
service clients to make API call on v2 endpoints.

Closes-Bug: #1667354

Change-Id: I9002c5ef8b4641597561d2b909bf5914ab8d9995
3 files changed