XXX:
 * cover more
 * slave: allow to set check-frontend-ip-list per each region, as globally per slave it makes no sense!!!!!
 * slave: publish check-frontend-ip-list and nameserver-list per each region
 * test adding a region
 * test removing a region

The requests are backward compatible, so for current and simple usage
automatic region is setup.

Much more information are published to main and shared instances, like
lists of available and assigned regions.