apps: Added uperf module

This is a nice tool that allows to simulate almost every workload:
 - Uses a pthread library to create multiple worklaod threads.
 - Uses poll() on a receive side.
 - Uses an XML configuration files for workload description.
 - Provides quite a lot workload statistics.

The open source tree has quite a lot of bugs, so I created a private tree
on a github and fixed a few of them already.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>