Initial submission of MQTT-related code to the Nmap project. - #352

Fun! I only just read about MQTT yesterday when looking for more TLS-secured protocols. I'll take a look at your submission.

Thanks! I'm hoping to add some more protocols in the coming weeks, all for a project in an Internet of Things course.

Some feedback:

• The IANA-reserved name for port 8883 is "secure-mqtt" so use that instead of "mqtt-tls" in the portrule and in nmap.services.
• You can use comm.tryssl instead of creating a new socket and setting timeouts yourself, and it will transparently use TLS when appropriate. To do this, you need to either expect a banner or have data to send at the time that you call tryssl, so you may have to change your abstraction a bit because the Helper class has that info, but the Comm class is the one that needs it.
• Update the datafiles to detect SSL on port 8883: add it to the ports line of SSLSessionReq and TLSSessionReq probes; add it to the LIKELY_SSL_PORTS in shortport.lua.
• Be sure to use the check script or commit hooks in the Code Standards page on SecWiki to check for globals. It found a typo on line 207 of the script, for instance.
• Could we get a reference link in the script description? I don't understand from the description what is the significance of the output.
• We'd like all time-related script args to be able to take things like "5000ms" and "3s". You can use stdnse.parse_timespec for this. Then use nmap.clock_ms instead of os.time to get a more granular clock.

Thanks so much for using @name in your NSEdoc! Object-oriented libs can make for ugly generated docs without this.

I'll make those changes today. Thanks for the quick turnaround on reviewing!

I have made the recommended changes, including the stylistic ones.

Did some minor cleanup, and added a bunch of tests for the very sensitive functions that are used for generating and parsing values.

It's been a while, wondering if there's anything that's needed from me that would help move this along?