Create two new clients under tempest.lib libary

There are two API v2 actions that only admin has the permission to excute,
according to:
http://developer.openstack.org/api-ref-blockstorage-v2.html#listPools
http://developer.openstack.org/api-ref-blockstorage-v2.html#showBackendCapabilities

Currently, those actions reside on BaseVolumesClient class and I think we
should separate them to new files: tempest/lib/services/volume/v2/capabilities_client.py
                                   tempest/lib/services/volume/v2/scheduler_stats_client.py

Partially implements blueprint consistent-service-method-names

Change-Id: I48e5e19331dd636a093e1817e5c2ea31534ae2c3
9 files changed