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

[smithfarm]

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 #465 for more context.