CDK-647: Update examples to use Flume's Log4jAppender and DatasetSink

 * This patch includes configuring the Log4jAppender to gracefully
    handle connection errors. This is useful as it avoids a circular
    dependency between loading the log4j configuration to create the
    dataset and starting Flume after the dataset exists.
 * The README for the logging, logging-webapp, and demo examples have
    been updated accordingly.
 * This patch also includes some fixes needed to work on the CDH5.1
    QuickStart VM. I suspect more of the examples may have issues.
    So I'll file a follow-up JIRA to check them out and to update the
    top-level README to account for changes between the 4.4 and 5.1 VMs.
I don't think we should switch to the dataset CLI in the examples until we can run it from the host (off-cluster). We have to support running the examples from both the host and the guest (off- and on-cluster) like we do today.

It looks like the hostname of the QS VM changed from localhost.localdomain to quickstart.cloudera in version 5, so we should update the instructions to add quickstart.cloudera to /etc/hosts on the host in https://github.com/kite-sdk/kite-examples#setting-up-the-quickstart-vm.

I've also been looking at parameterizing the hostname for some of the work I've been doing to get the examples working against a remote cluster, so I'll share that separately.