on Ubuntu 14.04.1 LTS if nsupdate runs without port number given it treated argument following server name as port number.
and throws error:
```
port 'update' is not numeric
syntax error
```
When `nsupdate -l` works, `-dnsapi nsupdate` requires no further
configuration. It does not use `nsupdate -l` (would imply more code
and more code changes), but points `nsupdate -k` at the key which
would be used by `nsupdate -l`.
