Move some of the custom requirements out of tox.ini

This change removes the need for an optional-requirements
file which isn't being kept up to date with the rest of the
openstack ecosystem and moves most of the customizations to
test-requirements and where different versions are still
needed (aka for SQLAlchemy) we place those varations into
there needed tox environment as required.

Change-Id: I443794b83de3f6a196fa7fc29a90620fb51b7f4c
Merge "Move some of the custom requirements out of tox.ini"