Comment 2 for bug 1674858

I think we can just set EnableConfigPurge in environments/major-upgrade-composable-steps.yaml the unset it in environments/major-upgrade-converge.yaml, e.g similar to how we're doing the upgrade flag in https://review.openstack.org/#/c/438044?

If that sounds reasonable we can add the flag to https://review.openstack.org/#/c/438044 or push a separate review (perhaps the latter since the two changes aren't strictly related?)