Collect Kubelet logs with Fluentd->(Elasticsearch|Fluentd->Cloud Logging)

This PR allows us to collect Kubelet logs. This PR:
* Modifies the manifest files for the Fluentd -> Elasticsearch and Cloud Logging images to map /var/log to allow /var/log/kubelet.log to be collected
* Modifies the Docker images for Fluentd collector containers to collect /var/log/kubelet.log and send to Elasticsearch or Cloud Logging (depending on the container)
@dchen1107