Allow for use_user_site being set to an integer
Allow for use_user_site being set to an integer

This can come from tox config, see:
https://github.com/pypa/pip/pull/7002#issuecomment-545108292

pfmoore/pip,sbidoul/pip,pfmoore/pip,xavfernandez/pip,xavfernandez/pip,pradyunsg/pip,pypa/pip,xavfernandez/pip,pypa/pip,pradyunsg/pip,sbidoul/pip