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 would suggest changing name of the property to:

```java
UseIPAddrForServer("UseIPAddrForServer"),
```