Accomodate services where zone name is not unique

fixes #167 per https://groups.google.com/forum/#!topic/denominator-dev/bi6EnsFISyY

You should now lookup record sets in the form:
```java

for (Zone zone : dnsApi.zoneApi()){
   rrsetApi = dnsApi.resourceRecordSetApiForZone(zone.idOrName());
   // do stuff
}

```