Mention API V2 should no longer be used
Mention API V2 should no longer be used

Adding a reminder that V2 APIs should no longer be used and are only
available for backward compatibility purposes.

Change-Id: Ib885c102a59b3c339b0e7986145a1c2defb346fc
Closes-bug: 1580552

rajalokan/nova,Juniper/nova,jianghuaw/nova,mahak/nova,gooddata/openstack-nova,rahulunair/nova,gooddata/openstack-nova,jianghuaw/nova,openstack/nova,klmitch/nova,phenoxim/nova,klmitch/nova,mikalstill/nova,Juniper/nova,jianghuaw/nova,rajalokan/nova,jianghuaw/nova,rahulunair/nova,mikalstill/nova,gooddata/openstack-nova,hanlind/nova,vmturbo/nova,rajalokan/nova,rajalokan/nova,Juniper/nova,vmturbo/nova,Juniper/nova,openstack/nova,klmitch/nova,vmturbo/nova,mahak/nova,hanlind/nova,mahak/nova,rahulunair/nova,mikalstill/nova,vmturbo/nova,openstack/nova,phenoxim/nova,klmitch/nova,gooddata/openstack-nova,hanlind/nova