* fn: introducing docker-syslog driver as default logger
With this change, fn-agent prefers RFC2454 docker-syslog driver
for logging stdout/stderr from containers. The advantage
of this is to offload it to docker itself instead of
streaming stderr along with stdout, which gets multiplexed
through single connection via docker-API.
The change will need support from FDKs in order to log
correct call-id and supress '\n' that splits syslog lines.
ad011fde7f