Use Block Storage API v3

Cinder is removing the Block Storage API v2 in Xena [0], so the
cinder rally job should use v3.

[0] https://review.opendev.org/c/openstack/cinder/+/792299

Change-Id: I9709b0c937ba355ee34624eb1640ad08f506922e

rally-jobs/cinder.yaml

@@ -3,7 +3,7 @@
 ---
   version: 2
   title: Task for gate-rally-dsvm-rally-cinder job
-  description: Testing mostly cinder related plugins
+  description: Testing mostly cinder related plugins using Block Storage API v3
   subtasks:
     -
       title: CinderVolumes.create_volume tests
@@ -36,8 +36,8 @@
               users_per_tenant: 2
             api_versions:
               cinder:
-                version: 2
-                service_name: cinderv2
+                version: 3
+                service_name: cinderv3
         -
           description: "Create a volume from the specified image."
           scenario: