Add volumev3 endpoint for Cinder

Change-Id: I97caa6bfababf7d1cc714296ae66f77d22bf24ab
diff --git a/lib/tempest b/lib/tempest
index fd98c94..0fc5815 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -425,6 +425,8 @@
     iniset $TEMPEST_CONFIG volume-feature-enabled incremental_backup_force True
     # TODO(ynesenenko): Remove the volume_services flag when Liberty and Kilo will correct work with host info.
     iniset $TEMPEST_CONFIG volume-feature-enabled volume_services True
+    # TODO(ameade): Remove the api_v3 flag when Mitaka and Liberty are end of life.
+    iniset $TEMPEST_CONFIG volume-feature-enabled api_v3 True
 
     if ! is_service_enabled c-bak; then
         iniset $TEMPEST_CONFIG volume-feature-enabled backup False