support legacy pip versions as well as version 10
support legacy pip versions as well as version 10

This adds "support" for pip version 10 and up, although it's going in
the direct opposite direction of what the pip people are promoting [1].
Anyway, for now we're interested in this functionality, so we keep it.

[1]: https://mail.python.org/pipermail/distutils-sig/2017-October/031642.html

cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo