TCP syslog writer should redial on connection lost (agent)

[umputun]

In case if dkll server failed/restarted and communication between agent and server is non-default tcp, agent writers can lose connection quietly. It has a repeater, but this one is on the dial stage only. and works on new container event.

[umputun]

I have tried several approaches:

1. Count on built-in retry mechanism from std syslog
2. Wrap syslog's write and handle failed writes with retry
3. Fail on write error and let docker restart the container
4. Replace syslog by gsyslog supporting timeouts

All of these changes solved the problem just partially, in the best case. I didn't have much time to hunt it down, but if anyone wants to investigate it and propose a working solution - PRs are very welcome.