* add validation is git found
* add validation is .git folder exists in project (project zip archive download without .git folder)
* get head commit SHA if git found and .git folder exists

Tested:
* configure project by CMake 3.0.0 successfully (with and without git), with project zip archive (without .git folder) and with project cloned from github
* configure project by command: cmake -G "Visual Studio 12 Win64"
* build solution by Visual Studio
* manually validate that file utils/build_version.cc contains valid head revision value