* Add option to silence warnings related to deprecation of Python versions
* Move skip_if_python2 and skip_if_not_python2 decorator declaratios to test/lib/__init__.py and use them in test_warning.py
* Add tests to ensure that python version deprecation warning is shown correctly and can be silenced by a flag.
* Add new test to ensure that --no-python-version-warning flag does nothing if python version is not 2