Add make variable for setting python 2 variable for cpplint

[syclik]

Summary:

cpplint requires Python2. Add a variable to set it from the command line.

Reproducible Steps:

When python defaults to Python 3, cpplint fails to run.

Current Output:

> make cpplint RUN_CPPLINT="python3 lib/cpplint_4.45/cpplint.py" 
make: *** [cpplint] Error 1

Current Version:

v2.9.0