tools: rewrite check-install.sh in python

As it is, check-install.sh does not show more helpful error messages,
and supporting various shells could be a problem. This patch rewrites
the same in Python.

This patch also enables check-imports.py in the linting process

PR-URL: https://github.com/nodejs/node/pull/6105


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>