Platform logging enhancements

Provide enhanced logging capabilities:

* Add a Syslog logger implementation
* Make MCollective request-scoped context available to logger impls via NodeLogger
* Allow request-scoped context to be attached to log events via configuration for SplitTraceLogger and SyslogLogger implementations
Merge pull request #4624 from ironcladlou/dev/syslog

Merged by openshift-bot