Refactor eslint.py and clang_format.py

The clang_format.py and eslint.py scripts share a lot of code. These have large amounts of duplicate code including the Repo class for using git, and the parallel_process function.

This code should be de-duplicated and moved into separate python modules.

Proposed Layout:
buildscripts/linters/

• __init__.py
• git.py - Repo class and related functions
• parallel - Parallel Process function

An example of why code de-duplication is bad is that the Repo class has diverged between these two files, and they now have different features.