tools: example_pull_lab.py use payload in tuxrun

This script takes pull-lab payloads and executes them in tuxrun. Tuxrun
handles the downloads and VM (QEMU/FVP) execution. It is based on script
that Denys Fedoryshchenko put a PR up. But adds more features with
Tuxrun to execute these payloads.

The script can be extended in future for different use cases. But right
now it detects arch from the job definition, supports ability to filter
by platform, group, device and runtime. Retry logic for failure uses and
uses --cache-dir for saving caches and outputs.

Future parts of the script will also include actual DUT's (Device Under
Test) instead of just virtual targets.

Signed-off-by: Ben Copeland <[email protected]>

Author: bhcopeland