setup.py not compatible with pip 10+

[mtfurlan]

setup.py uses pip as a module, which is not how pip wants to be used so they changed the internal API to force people to use pip correctly. https://github.com/pypa/pip/issues/5154#issuecomment-378197307

$ ./var/bin/pip --version
pip 19.0.2 from /tmp/git-repo/var/lib/python3.5/site-packages/pip (python 3.5)
$ ./var/bin/pip install -r requirements-test.txt 
Obtaining file:///tmp/git-repo (from -r requirements-test.txt (line 2))
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/git-repo/setup.py", line 169, in <module>
        install_requires=requirements(),
      File "/tmp/git-repo/setup.py", line 125, in requirements
        requirements = pip.req.parse_requirements(
    AttributeError: module 'pip' has no attribute 'req'
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/git-repo/