If a pod has not printed anything to stdout/stderr, it's expected
behaviour to get `-- No entries --`, even when requesting json output.
Prior to this change, a warning would be printed in such an occasion.
Add GeneratePodHostNameAndDomain() to RuntimeHelper to
get the hostname of the pod from kubelet.
Also update the logging flag to change the journal match from
_HOSTNAME to _MACHINE_ID.
This enables more fine-grained control over the things we want to
output. Also by closing the stdout/stderr of the journalctl process
when user hits `Ctrl-C` after `kubectl logs $POD -f`, this enables
the journalctl process to exit.
