[COMMON] Adds 2 upper-constraints files to pin all dependencies

[COMMON] Adds 2 upper-constraints files to pin all dependencies

It leverages the latest change from lfdocs-conf and the
upper-constraints.txt now centralized in ONAP docs.
In a long run, upperconstraints.os.txt should be removed once ONAP
is synced with OpenStack.

docs/requirements-docs.txt is renamed requirements.txt as it mixes
both docs and linter dependencies.

It removes tox and setuptools from requirements as nothing depends on them
(most requirements should be removed except lfdocsconf)

Issue-ID: DOC-765

Change-Id: Iae808297484f4798de82a43597ccad7905ff4c94
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>