paths: use `list_paths` in `hg paths`
Using common code will make it simpler to update the logic behind the path
definition and storage.
Differential Revision: https://phab.mercurial-scm.org/D10441
# name space package to host third party extensionsfrom __future__ import absolute_importimport pkgutil__path__ = pkgutil.extend_path(__path__, __name__)