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
diff --git a/tempest/clients.py b/tempest/clients.py
index 53f3775..42bd8f5 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -307,6 +307,10 @@
             self.volume_v2.AvailabilityZoneClient()
         self.volume_limits_client = self.volume_v1.LimitsClient()
         self.volume_v2_limits_client = self.volume_v2.LimitsClient()
+        self.volume_capabilities_v2_client = \
+            self.volume_v2.CapabilitiesClient()
+        self.volume_scheduler_stats_v2_client = \
+            self.volume_v2.SchedulerStatsClient()
 
     def _set_object_storage_clients(self):
         # Mandatory parameters (always defined)