Remove volume v1 API service client usage

Volume v1 API has been gone since long and Tempest also
marked their deprecation since Juno
- https://review.openstack.org/#/c/446238/

Now Tempest is removing the deprecated config option and
alias for voluem v1 service client in
- https://review.openstack.org/#/c/573135/

Before the Tempest patch gets merged, we need to remove all usage
of volume v1 things.

Change-Id: Iac5d1914814afbe81f3d83c875620931884584cd
Needed-By: https://review.openstack.org/#/c/573135/
diff --git a/ironic_tempest_plugin/manager.py b/ironic_tempest_plugin/manager.py
index 9967a5d..b529e3c 100644
--- a/ironic_tempest_plugin/manager.py
+++ b/ironic_tempest_plugin/manager.py
@@ -81,12 +81,10 @@
         cls.security_group_rules_client = (
             cls.os_primary.security_group_rules_client)
 
-        if CONF.volume_feature_enabled.api_v2:
-            cls.volumes_client = cls.os_primary.volumes_v2_client
-            cls.snapshots_client = cls.os_primary.snapshots_v2_client
-        else:
-            cls.volumes_client = cls.os_primary.volumes_client
-            cls.snapshots_client = cls.os_primary.snapshots_client
+        if (CONF.volume_feature_enabled.api_v2 or
+            CONF.volume_feature_enabled.api_v3):
+            cls.volumes_client = cls.os_primary.volumes_client_latest
+            cls.snapshots_client = cls.os_primary.snapshots_client_latest
 
     # ## Test functions library
     #