Running "openstack undercloud install" attempted to delete and recreate the Undercloud's neutron subnet even if the subnet required no changes. If an Overcloud was already deployed, the subnet delete attempt failed since the subnet contained allocated ports. This caused the "openstack undercloud install" command to fail. This fix changes this behavior to only attempt to delete and recreate the subnet if the "openstack undercloud install" command has a configuration change to apply to the subnet. If an Overcloud is already deployed, the same error message still occurs since the director cannot delete the subnet. This is expected behavior though since we do not recommend change the subnet's configuration with an Overcloud already deployed. However, in cases with no subnet configuration changes, the "openstack undercloud install" command no longer fails with this error message.