Use new Network.are_host_same() equivalency check

Replace the existing "is localhost" checks with the new, more reliable method.

Also, update the slave-registration validation logic to use the rsa_keys as the unique identifier for a host, rather than the hostname. This PR should significantly improve "clusterrunner deploy" robustness.
I think you can use the "new" argument of `self.patch()` to temporarily switch methods. Try:
```python
self.patch('app.util.network.Network.rsa_key', new=rsa_key)
```