Update setuptools to 5.0.2.  5.0 causes build failures for at least some Linux distributions, including Ubuntu 12.04

Testing Done:
./build-support/bin/ci.sh

This has some failures, but they're all also present on master.

Bugs closed: https://github.com/pantsbuild/pants/issues/317

Reviewed at https://rbcommons.com/s/twitter/r/630/