Add ipv6 config

This is a first pass at adding the necessary changes to fully enable ipv6 in the open source Chef server.

It is entirely possible something has been missed and this still needs to be run through vigorous testing, but I wanted to get the code out for review.

/cc @sdelano @marcparadise @manderson26 @tylercloke @oferrigni  @hosh @jkeiser @josephrdsmith and anyone else who might be interested.