Add script for updating requirements

This is a hacky little script for pulling all of the requirements
from each project into a consolidate pair of pip-requires and
test-requires files.

The output of this can't be passed to 'pip install -r' without
some further sanitation to clean up duplicates.

Change-Id: I47159f744086dc1de1b9fa07ef4cc5a0f85087b0
Merge "Add script for updating requirements"