Set openrc with OS_VOLUME_API_VERSION with cinder v2

As recently Nova merged commit https://review.openstack.org/#/c/124468/
which have switched to use Cinder v2 api, and cookbook will register
Cinder v2 endpoint. So openrc file also need to be updated
for cinder v2 support.

Change-Id: I3bcd3ca95d5f65c33eb5ddfda611280785412549