(no-ticket) Use requirements.txt in favor of dependency_links

Current release of setuptools and pip deprecate dependency_links
(as insecure...). Simple 'pip install -e .' must be now called as
'pip install --process-dependency-links -e .', which still prints
a red warning that dependency links will be removed in the next
release.

Change-Id: If694093420a2d41b25a070e2de9a5b8813633ed8
Merge "(no-ticket) Use requirements.txt in favor of dependency_links"