Azure/GitLab: Ensure we use requirements.txt for testsuites

Given that test/py/requirements.txt has all required test modules, make
use of that rather than a manual pip install list before running our
assorted tool testsuites.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>