Properly communicate dependencies to PyPI

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Include requirements-dev.txt in MANINFEST.in

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Drop version restriction on requests module

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>