python: Recreate test/py and tools/buildman requirements.txt files

python: Recreate test/py and tools/buildman requirements.txt files

Use the "pipreqs" tool to re-create these files, with a few manual
corrections. We still need to include pytest-xdist which the tool does
not detect. We also for now don't upgrade most of the required tools as
that creates problems with various tests, which should be resolved
independently.

Signed-off-by: Tom Rini <trini@konsulko.com>