Use the rdo havana repo with the RHEL family

In devstack viewpoint there is not too much differences at the moment.
But using the grizzly named repo close to havana release, was strange to me.

Switching to the repo link which does not have a version like '-3'.

Change-Id: Ib421d50d19baeeeff264aa0cb9c105fffcf572f8
Merge "Use the rdo havana repo with the RHEL family"