Set openstack_old_version to openstack version by default

openstack_old_version is used only during upgrade/update procedure.
By default openstack_old_version should be the same as openstack_version
and not hardcoded. Currently it is always ocata, but with this patch
it can be easily overriden from cluster level. The same also is
applicable for Gnocchi.

Change-Id: I7dfe83838d9e52900b6ac264228fa0d448193c94
Related-Prod: https://mirantis.jira.com/browse/PROD-24991
1 file changed