Replace rsyslog for non-bootstrap agents

This PR uses a fork of the standard syslog package to stream logs directly to state machine rsyslog daemon, without the need for a local rsyslog install.

The forked version of syslog allows TLS connections, and works from Windows.
Done. https://github.com/juju/syslog

Please follow up with @bz2 & @sinzui to ensure it's supported by CI and the landing bot.