Logstash conf fixes

- use UTF-8 explicitely
- del experimental syslog_pri plugin usage,
- fix grok patterns,
- add grok for OS traces

Change-Id: I698179fce2b5e8b9b4308c14da5c75a06b35908f
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>