Currently, pre-flight validations are run right after install-config syntax validation. That is, before manifests are generated.

This card is about moving the pre-flight validations after the "create manifests" target.

Expected outcome:

With this change, the Installer will not need to connect to OpenStack until after the manifests are created (unless the install-config interactive wizard is used).

Also potentially renders OPENSHIFT_INSTALL_SKIP_PREFLIGHT_VALIDATIONS variable useless.

cf:

• https://github.com/openshift/installer/pull/4452#issuecomment-738859219
• https://github.com/openshift/installer/pull/4452#pullrequestreview-545235420