ceph-salt needs to assert that hosts don't think their own IP address is a loopback address

As a pre-flight check before "apply", ceph-salt should check what each host returns for

```
socket.gethostbyname(socket.gethostname())
```

If the value returned by this looks like a loopback address (IPv4 or IPv6), error out and tell the user to fix it.

See the code and comments in https://github.com/ceph/ceph-salt/pull/465 for more context.

Start by locating the pre-flight checks run before "apply" and review the context in pull request 465. Trace how each host evaluates socket.gethostbyname(socket.gethostname()), then add coverage for IPv4 and IPv6 loopback results and verify that the check reports an actionable error.

Written by the indexing model from the issue text.