Refactored endpoint constants, tests

Here are the new, normalized and refactored endpoints for each service:

```
RACK_API_URL
US_IDENTITY_URL
UK_IDENTITY_URL
BLOCKSTORAGE_DFW_URL
BLOCKSTORAGE_ORD_URL
BLOCKSTORAGE_LON_URL
SERVERS_DFW_URL
SERVERS_ORD_URL
SERVERS_LON_URL
DATABASES_DFW_URL
DATABASES_ORD_URL
DATABASES_LON_URL
LOADBALANCERS_DFW_URL
LOADBALANCERS_ORD_URL
LOADBALANCERS_LON_URL
ORCHESTRATION_DFW_URL
ORCHESTRATION_ORD_URL
ORCHESTRATION_LON_URL
ORCHESTRATION_IAD_URL
DNS_DNS_URL
DNS_LON_DNS_URL
NETWORKING_DFW_URL
NETWORKING_ORD_URL
NETWORKING_LON_URL
```

Tests updated to use `Fog::Rackspace::SERVICE` *or* `Fog::SERVICE::Rackspace` format