Make the DC names in DNS names always be two characters and never collide

[yaronyg]

Right now we create the data center name segment of a DNS name by taking the first characters of the DC's name. In most cases those are two characters but in some cases it is three characters. And there is at least one pair of DCs that have the same two character string!

What we need is a mapping table that guarantees the name will always be exactly two characters without collisions.

The reason for 2 characters is just space. We could go to three. But some names are only 24 characters long and we need to fit a lot in there.