platform: add a new jsonpoll command.

Chimera will run a web server that exports stats for the radio and modem
(like temperatures, tx/rx counters, etc) via a RESTful JSON web interface.

jsonpoll periodically connects to that web server (known for now as
Glaukus Manager) and requests stats. jsonpoll then writes the response
out to disk (under /tmp/glaukus/) for catawampus to then read and export
via cwmp.

Unit tested and lint-free. Will need to include this in buildroot as a
next step. Further work will entail creating and updating additional
JSON requests.

Change-Id: Id4cc2f0ac55a5678569fd4604a3ece8f5bc005d8
4 files changed