Directly support extend user details in the Meterpreter API

[jmartin-tech]

Summary

Meterpreter API extension to support user structure details, a specific example would be user and group details for a Linux/Unix environment.

Basic example

(uid=0, gid=0, euid=0, egid=0)

Motivation

The current meterpreter API provides sys.config.getuid which returns a TLV_TYPE_USER_NAME and is utilized to compare String usernames in various places. When this was implemented in the latest generation linux meterpreter (mettle) this was extended to provide these details, however is not really the username. To consolidate the API and still retain this useful data a new method call would be desired.