add ability for ribbon/eureka to use ipAddr instead of hostName configed...

add ability for ribbon/eureka to use ipAddr instead of hostName configed via Archaius

this relates to the discussion on the mailing list here:

https://groups.google.com/forum/#!topic/eureka_netflix/7M28bK-SCZU
I will look at this next.  I will note that for IBM's needs (and I'd think many others), but able to set it globally would be the most typical case.