[#1360] Get git executable path on all platforms.

Problem description
===================
On windows git executable should be search also using PATH not only in hardcoded locations


Why we got into this (5 whys)
=============================

On windows git was searched only on hardcoded locations.


Changes description
===================

Now git executable is searched also using PATH on all operating systems.
Now if git is not installed on unix, then an exception is also raised.


How to try and test the changes
===============================

reviewers @adiroiban @alibotean 

What code / repositories were affected. Where is the code.
If the code in only on a single feature branch, no need to say something
about the code.

For testing on windows git must be installed on non default location. It must also be added to the environment PATH variable.