deps: check in gtest, add util unit test
Check in a gypified gtest and add a simple unit test to show that the basic infrastructure is in place.
Refs: https://github.com/iojs/io.js/issues/1193
R=@indutny and /cc @jbergstroem
https://jenkins-iojs.nodesource.com/view/iojs/job/iojs+any-pr+multi/333/