mod_log_json: Prefer native Lua table.pack over Prosody util.table one Prosody is removing support for Lua 5.1, which was the reason for util.table.pack to exist in the first place, since Lua 5.2+ provides table.pack. In prosody rev 5eaf77114fdb everything was switched over to use table.pack, opening the door for removing util.table.pack at some point. This change here is to prepare for that future eventuality.

Generate a DNS UPDATE order in format suitable for `nsupdate` based on
current port configuration.

Example output:

```
$ prosodyctl mod_dnsupdate -d example.com -t xmpp.example.com example.com
zone example.com
server ns1.example.com
ttl 3600
add _xmpp-client._tcp.example.com IN SRV 1 1 5222
add _xmpp-server._tcp.example.com IN SRV 1 1 5269
```