make build_configuration test happy on OSX, not just linux

"Looks like we need to toss in a realpath somewhere in these tests" was true

Also a couple of missing deps reared their head when I ran this test on its own

Testing Done:
./pants goal test tests/python/pants_test/base:build_configuration

./build-support/bin/ci.sh # on my mac

Linux still happy
https://travis-ci.org/pantsbuild/pants/builds/30092011

Reviewed at https://rbcommons.com/s/twitter/r/694/