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.
We actually want to limit the number of build tags we use, to keep as much of the code testable from linux as possible.  It's occasionally a little uglier, but it means a lot more LOC will get tested from our devs (who are all on linux).