Add socket event logging to event broker

Mqexec logs when connections are accepted/broken, and it's been
very helpful in diagnosing problems. This commit adds that
to the event broker.
Change event broker logging to nagios log functions

The NagMQ event broker has always logged very sparsely to syslog,
which drops messages and confuses users by having to look in
a different place for NagMQ messages than for Nagios messages.

This commit changes error/warning messages to use the Nagios log,
and the debug messages to go to the nagios debug log.