When docker runs in daemon mode, send kill -HUP to it restarts all the container.

While the logging driver is in the work #7195, and for simple setup, it would help considerably to be able to use logrotate with something like /var/lib/docker/containers/*/*.log to rotate the log. This path works fine with log rotate, but the missing thing is to be able to signal docker to reopen the xxx-json.log.

Sending SIGHUP or SIGUSR1 should reopen all log files.